
Glass. 
Book, 



COPYRIGHT DEPOSIT 







Btast FurnACG 

Harbison -Walker 
Refrs.ctoriOvS Co. 

PiH^bui^k, Pec. 






Ok 



y 



Copyright, 1911, by the 
Harbison-Walker Refractories Co. 



i^~ ns 



©CI.A303131 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 



CONTENTS 

Introductory 9 

Map in colors showing Blast Furnace Districts and Iron 
Ore Deposits of the United States attached to inner 
back cover. 

Chapter I. — Description of Plant. 

page 

General Sketch 11 

Furnace — Hearth or Crucible 14 

Bottom 14 

Tapping Hole 16 

Cinder Notch 1G 

Tuyeres 18 

Tuyere Stocks 21 

Bustle Pipe ........ 21 

Hot Blast Main 21 

Bosh Construction and Lining .... 22 

Bosh Cooler Plates 23 

Mantle 24 

Inwalls 24 

Top ... 25 

Filling Device 26 

Stock Distributors 26 

Openings . 27 

Piping 29 

Downcomer . . ■ 29 

Dustcatcher 30 

Gas Mains 30 

Boiler Plant 31 

Blowing Engines 31 

Cold Blast Main 32 

Hot Blast Stoves — General Description . . 32 

Valves 37 

Disposal Equipment 52 

Pig Beds. . 52 

Chills 54 

Casting Machine 54 

Slag Disposal 55 

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Harbison-Walker Refractories Co., Pittsburgh, Pa. 

Chapter II. — Materials — Ores. page 

Ores 

Hematites 58 

Brown Ores 61 

Magnetites 62 

Carbonates 64 

Summary of Production 65 

Items Affecting Valuation 68 

Treatment of Ores. 

Roasting 71 

Calcining 75 

Concentration 77 

Nodulizing 80 

Briquetting 82 

Chapter III. — Materials — Fluxes and Fuels. 

Fluxes — Composition 84 

Relative Value 87 

Fuels 

Coke 92 

Impurities 93 

Manufacture— Beehive Oven ... 98 

Mitchell or Belgian Oven 101 

By-product Oven . . 102 

Charcoal. . f 104 

Anthracite Coal ........ 105 

Valuation of Fuel 106 

Chapter IV. — Burdening the Furnace. 

Introductory 108 

Slag 109 

Composition 112 

Control 113 

Detail of Problem in Burdening . .116 

Flux 117 

Fuel 117 

Ore 118 

Fuel Requirements 119 

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Harbison-Walker Refractories Co., Pittsburgh, Pa. 

Chapter Y. — Operating the Furnace. page 

Blowing in 122 

Charging 125 

Operation 126 

Banking the Furnace 129 

Blowing out 131 

Operation of Stoves 131 

Furnace Troubles 134 

Destruction of Lining 134 

Break-outs 138 

Loss of Tuyeres and Cooler Plates . . .138 

Pillaring 139 

Scaffolding 140 

Wedging 141 

Chilling 142 

Chapter VI. — Furnace Reactions. 

General Discussion 144 

Flux 147 

Fuel 150 

Ore 150 

Cyanides 157 

Carbon Ratio 158 

Dry-Air Blast 159 




INTRODUCTO FC Y 



I N the effort to work along the lines 
making for maximum efficiency, we 
have long realized the benefit of hav- 
ing the members of our organization 
as familiar as possible with at least the under- 
lying principles concerning the various industries 
in which fire brick and other refractories form 
so vital a part of the equipment. U A Study 
of the Blast Furnace" was prepared with 
this end in view, and is merely a digest in 
as simple and brief a form as possible, of the 
widely scattered information relating to blast 
furnace operation that has appeared in the 
technical press. 

Of necessity, there is little of original investi- 
gation contained in this volume. All available 
information has been most freely drawn upon, 
particular indebtedness being acknowledged to 
the government reports on "The Production of 
Iron Ores," to Forsythe's work, "The Blast 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

Furnace and the Manufacture of Pig Iron,' 1 
and to Campbell's volume, "The Manufacture 
and Properties of Iron and Steel." 

As mentioned in the preface of "A Study of 
the Open Hearth," the present volume forms 
the second of the series. 



10 





DESCRIPTION of PL ART 

CHAPTER I 
FURNACE 

eneral Sketch — The blast furnace, 
| in which is conducted the manufac- 
ture of pig iron, is merely a cylin- 
drical steel shell lined throughout with 
fire brick. This shell varies in height from 40 
to 100 feet or even higher, and in each furnace 
has varying diameters from top to bottom, the 
lines of the furnace being thus adjusted to 
the various changes going on within it. The 
walls of the hearth near the bottom of the fur- 
nace are pierced with openings through which 
so-called tuyeres supply a strong blast of heated 
air to unite with the carbon of the fuel. 

Into the furnace top is charged continuously 
the ore, fuel and flux which go to make up the 
burden. 

The ore furnishes the iron for which the 
furnace is operated; the fuel in combustion 
gives off gases which serve to reduce the iron 



11 



Harbisox-Walker Refractories Co., Pittsburgh, Pa. 

to a metallic form, and also supplies the heat 
necessary for the reactions which occur within 
the furnace, and to melt the resultant products. 
The flux serves to unite with various com- 
pounds which would otherwise be infusible at 
furnace temperatures and so, not only removes 
in a fluid state the ash of the fuel but the earthy 
materials and impurities occurring in the ore. 
It also serves in such combination as the means 
of controlling the amounts of certain elements 
desirable in the iron, but desirable only within 
limited percentages. 

As the charge slowly works its way down- 
ward, approaching the zone of highest 
temperature at or slightly above the tuyeres, 
the various reactions become more and more 
complete and, finally, fusion of the resultant 
products occurs, the molten material collecting 
in the hearth of the furnace, which serves as 
a reservoir. The molten iron being of greater 
specific gravity than the impurities, sinks to 
the bottom while the impurities of the ore and 
ash, together with the flux, combine to form 
a slag which floats on the surface of the iron. 
The two can then be easily tapped off separately 
through openings located at proper levels. 

The gaseous products rising through the 
descending column of ore, flux and fuel, pass 
off through openings at the top and being 
combustible, are led through the downcomers 
to the hot blast stoves and to the boilers where 
they are burned. 

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Harbison-Walker Refractories Co., Pittsburgh, Pa. 




DIAGRAMMATIC SKETCH SHOWING PIPING FOR FURNACE AND STOVES 

13 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 

The diagrammatic sketch shown on page 13 
will illustrate the passage of the gases and 
the order in which the general construction 
will be considered. 

The furnace structure, a representative type 
of which is shown on page 15, will be considered 
under the three main divisions of: 

Hearth or Crucible, 
Bosh, 

( Lower Inwall 
Inwalls. < Middle Inwall 

( Upper Inwall or Top 

Hearth or Crucible — This portion of the 
furnace serves as a receptacle for the molten 
slag and iron. Its fire brick lining is from 
27" to 313^" in thickness or even thicker, 
dependent on the size of the furnace. It is 
surrounded by a steel jacket either of heavy 
riveted plate or still heavier castings of steel 
or iron in segmental form. In the first instance, 
the plate is often cooled by a direct water spray, 
while in the second, the castings are some- 
times made sufficiently heavy- to require no 
cooling, or if cooled, this is done by a trough 
of water running around the exterior. In a 
number of furnaces, pipes for cooling water are 
cast in the interior of the metal composing the 
hearth jacket itself. Page 17 shows a section 
of the hearth and bosh of a typical furnace. 

Bottom — The bottom is composed of a 
solid mass of fire brick, either in the standard 
sizes or in heavy blocks. The thickness varies 

14 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 




15 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 

with the size of the furnace, from 5' to 6' 
in the case of the smaller furnaces, to 12' or 14' 
in the larger furnaces, and must be very closely 
laid. If this is not done or if the joints are not 
properly broken, the molten metal tends to 
seep through the cracks and an enormous 
amount may so escape from the hearth. The 
high grade fire brick are underlaid by fire 
brick of a cheaper grade and this in turn by 
concrete in a deep and broad foundation, 
giving absolute stability. 

Tapping Hole — This is the opening through 
which the iron is drawn off and is usually 
located from 18" to 2' above the furnace bottom, 
and at the front of the furnace or facing the 
pig bed or cast house. It is merely an open- 
ing several inches square left in the brickwork 
and is not usually water-cooled, as in case there 
should be any leakage of water disastrous 
explosions would be sure to result on contact 
of the water with the iron. Except when 
the furnace is being tapped, the opening is 
closed with a semi-plastic clay mix which soon 
burns into place so that it is as firm as the 
hearth walls themselves. 

Cinder Notch — There is usually but one 
cinder notch, although there may be two or 
three in the larger furnaces. As its name 
implies, this opening is for the removal of slag 
or cinder and is placed at from 45° to 90° from 
the tapping hole. Since cinder only is to be 

16 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 




SECTIONAL VIEW 

BLAST FURNACE HEARTH AND BOSH 



17 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

drawn from it, it is evident that its height 
determines how high the iron may reach before 
tapping; in other w^ords, with any given 
furnace diameter, the cinder notch is so placed 
as to allow accumulation of the desired quantity 
of metal before tapping. It is water-cooled, 
being made up of a series of hollow tapered 
bronze, copper, or cast-iron coolers in the shape 
of a frustum of a cone. Page 19 shows the 
several parts, the outer and largest being usually 
termed the cooler, the next smaller the inter- 
mediate cooler, and the innermost, reducing the 
diameter to 2" or 23/£", is called the monkey. 
This small opening is stopped by a tapered iron 
plug attached to an iron bar by which it may 
be withdrawn w r hen it is necessary to flush off 
the slag. 

To each cooler are connected two water 
pipes for ingress and egress, thus allowing a 
good circulation and consequent cooling. Should 
the iron be allowed to rise high enough to reach 
these coolers, it would rapidly cut them out, 
as such is the effect of molten iron on copper 
or bronze. On the other hand, the slag while 
not affecting the bronze, would very rapidly 
cut away the brickwork, were no cooler in place. 
Molten iron itself has comparatively little 
effect on the fire brick. 

Tuyeres — The tuyeres through which the 
blast is admitted are symmetrically placed 
around the circumference of the hearth and 

18 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 




CiNDER NOTCH 




d^ ]{ — 'p> 



BOSH COOLER PLATE 



19 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

determine the height to which the slag may 
be allowed to rise. This may be anywhere from 
2^' to 4' above the cinder notch. The 
number of tuyeres varies widely with the ideas 
of the designer and the size and practice of 
the particular furnace. There are usually from 
10 to 16. The tuyere with its cooler is shown 
on page 17. 

The outer ring is termed the cooler and is 
practically identical with the cooler on the 
cinder notch except that it is flush with the 
interior and usually with the exterior wall. Into 
it fits the tuyere proper, projecting somewhat 
into the furnace. It also is hollow and cooled 
by water circulation in the same way. The 
size of the tuyere opening is important because 
of the direct relation it bears to penetration, 
pressure and volume of blast; it varies roughly 
from 33/2" to 7" in diameter. 

Against this inner tuyere rests a horizontal 
cast-iron pipe termed the blow-pipe, connecting 
in its turn with a pipe called the down-leg, 
tuyere stock, or boot-leg, which takes off from 
the bustle pipe encircling the furnace and sup- 
plying its blast. The blow-pipe is not lined 
and merely fits into place with a ball and socket 
joint, ground at each end, and is supported by 
the pressure of the tuyere stock, the latter 
swiveled and attached to the furnace bands 
by a strong spring. 

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Harbison-Walker Refractories Co., Pittsburgh, Pa. 

Tuyere Stock — As indicated on page 18 
this carries the blast from the bustle pipe to the 
blow-pipe. It is usually in two sections of 
cast iron and has a 2" to 3" lining of fire brick. 

Directly in line with the blow-pipe is a 
perforation or eye-sight in the back of the 
tuyere stock. This opening is closed by a 
piece of glass or mica so that an inspection of 
conditions in the hearth can easily be made 
and also a bar be thrust through, if necessary, 
from tuyere to tuyere, to dislodge any slag 
or other obstruction which may be closing the 
tuyere opening. 

Bustle Pipe — This is a cylindrical sheet 
steel pipe lined with from 9" to 12" of fire brick, 
and encircles the furnace about 10' to 15' 
above the floor. It is usually suspended by 
brackets or straps from the furnace columns. 
Its diameter is proportioned to the volume of 
blast it is to carry. 

Hot Blast Main — This is a fire brick 
lined pipe carrying the hot blast directly from 
the stoves and terminates in the bustle pipe. 
Its lining is from 9" to 12 " in thickness, and the 
selection of a brick suitable for the conditions 
encountered here and in the bustle pipe and 
tuyere stocks is most important. On the 
"hot side" of the furnace, as this system of 
piping is termed, the lining is subjected to 
high as well as varying temperatures and must 
be hard and tough to resist the scouring effect 

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Harbison- Walker Refractories Co., Pittsburgh, Pa. 

of the blast often laden with dust as it comes 
from the stoves. On the other hand, it must 
not be so dense as to spawl and crack from 
sudden changes in temperature and must at 
all times possess ample refractoriness. 

Bosh — Lining — This portion of the 
furnace, see page 17, is that extending from the 
upper line of the hearth about to the mantle 
or to the lowest portion of the inwall. It is in 
the form of an inverted frustum of a cone, 
its limits being termed the upper and lower 
bosh lines respectively, and is of one of two 
types of construction. The more usual is that 
showm on page 17 and practically all the 
larger furnaces are so constructed. No shell 
proper covers this but the brickwork is built 
up to the desired lines and is then supported 
by numerous very heavy steel bands completely 
encircling the bosh. In the brickwork, 27 " 
or more in thickness, there are inserted every 
few courses between the bands above referred 
to, bronze or copper cooling plates with a cir- 
culation of water. 

In the other type of bosh construction, 
no interior cooling plates are used, and but a 
thin layer of fire brick, say from 9" to 133^ ". 
Around this is a continuous steel shell cooled 
by troughs of water, the water flowing down 
from one trough to that below, or the trough 
may be riveted on in spiral shape, thus merely 
allowing the w^ater to circulate around the shell. 

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Harbison-Walker Refractories Co., Pittsburgh, Pa. 

However, boshes lined in any other way than 
with interior cooling plates are becoming fewer. 

The bosh as a whole is the zone of fusion, 
and the stock, as it approaches this zone, be- 
coming more and more pasty, occupies less 
and less space and finally melts. The narrow- 
ing lines of the bosh thus aid in concentrating 
the softening and semi-molten mass before the 
tuyeres, as well as afford it support. 

Bosh Plates — There are a number of styles 
of plates differing, however, but comparatively 
little, such as the Scott, Gayley and Kennedy 
plate. All are of bronze or copper, iron being 
a poorer conductor of heat, and melting or 
burning away much more readily. A typical 
plate is shown on page 19. In general, in the 
Scott plate, the water entering the plate is 
led directly to the nose, finding its w r ay back 
through a series of baffles; the Gayley has 
but one w^ater-w T ay, and that but 10" to J2" in 
depth from the nose, while the Kennedy is 
similar to the Gayley, but with two water- 
ways. The plates are usually of the same 
length as the thickness of the wall, but in order 
to save somewhat on the original cost, they 
are sometimes made but half this length, the 
remaining thickness of the opening in the wall 
being taken up by a cast-iron box open at each 
end through which this short plate slips to the 
interior wall of the furnace. This construction 
also makes somewhat easier the renewal of any 
plate, should it be burned out. 

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Harbison- Walker Refractories Co., Pittsburgh, Pa. 

Mantle — Just above the upper limits of 
the bosh is the mantle. This is circular in 
form, usually built up of heavy steel plates 
and angles and on it rests not only the entire 
weight of the furnace shell proper but the 
immense mass of brick lining beside. This 
mantle in turn is supported by a series of 
columns either of cast-iron or built up of struc- 
tural shapes, the foundations of these columns 
going down below the hearth level often to the 
furnace foundation itself. Such construction 
allows the entire hearth and bosh of the furnace 
to be torn down without disturbing any of the 
work above the mantle. 

Inwalls — The inwalls comprise those por- 
tions of the furnace from the mantle up, and in 
turn are often considered as being divided into 
the lower inwall, say the first 25', the middle 
inwall the next 20' to 25', and the upper inwall, 
or top. This entire portion of the furnace is 
surrounded by the usual riveted steel shell, 
the lining being from 27 " in thickness to even 
60 " at the mantle, as is the case in some of the 
large furnaces. From here, the thickness of 
the walls tapers somewhat toward the top. 

From the mantle up for varying distances 
there are often cooler plates embedded in the 
furnace walls. This practice is unquestionably 
extending and the tendency is to carry the 
plates higher and higher. These in a measure 
serve to protect the brick from cutting out 
under the severe conditions of modern driving. 

24 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

At the top of the furnace, the bell and 
hopper, i.e., the charging device, close the 
opening, and for some distance below this, 
the portion termed the stock line, the walls may 
be vertical. Often the slight outward flare 
of the furnace lines is continuous from the top 
entirely to the upper bosh line, this flare allow- 
ing freedom of movement for the descending 
charge. 

Tops — The blast furnace of the earliest 
type was left entirely open at the top, allowing 
the gases to burn freely, but there was soon a 
realization of the heat wasted and the top was 
then closed with a bell and hopper, as on page 
15. The hopper forms merely an annular 
Y-shaped bin at the top of the furnace and 
holds the accumulation of the charge until the 
proper time to dump it. 

The bottom of this hopper or bin is formed 
by the bell which effectually seals the opening 
until such time as the bell is lowered to discharge 
its contents into the furnace, but has the defect 
of allowing the escape of gases during that 
period. 

To overcome this, a second smaller bell 
was introduced, as on page 15. The skip 
dumps first upon this smaller bell which, in 
turn, lowers to allow the charge to slide to the 
larger bell, from which it discharges into the 
furnace. The whole arrangement being en- 
closed in one casing, there is no opportunity for 

25 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 

the escape of gases. The bell is of very heavy 
cast steel or iron, with the sides at an angle of 
about 45° so that the charge may easily slide 
off, and is lowered sufficiently to clear the 
engaging ring by some 18 " to 24 ". 

Filling Devices — In the old type of 
furnace where the tonnage was small, the fur- 
nace was hand-filled, i.e., the charges of fuel, 
flux and ore were wheeled in buggies from 
the bins to a vertical elevator beside the furnace 
stack. 

The buggies being hauled to the top, the 
top fillers emptied them, returning them to 
be refilled. With the advent, however, of the 
modern furnace of large capacity, it became 
more difficult to supply the fuel, flux and 
ore fast enough to take care of the furnace 
requirements. 

Furnaces are now designed with an auto- 
matic skip arrangement whereby the skip is 
hauled up an inclined skipway extending from 
the storage bins at the base to the furnace top 
and there automatically dumped. This arrange- 
ment, however, has introduced a number of 
complications which will be discussed later. 

Stock Distributors — As previously men- 
tioned, the advent of the automatic skip-filling 
arrangement introduced difficulties not at first 
recognized but which have been very wide- 
spread. It is apparent that as the skip dumps 
into the hopper of the receiving bell the coarsest 

26 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

lumps of ore, stone, etc., will roll faster than the 
fines, and accordingly tend to gather at the side 
opposite the skip. The same tendency holds 
good as the ore is dropped to the stock in the 
furnace. The result is that there is a prepon- 
derance of the coarser ore on the side of the 
furnace opposite the skip and, consequently, 
less resistance to the passage of the gases, re- 
sulting in an increase in the volume of gas 
passing up this side of the furnace. This 
produces greater heats and results in a tendency 
to erode and cut away the lining, creating a 
so-called "hot spot" which necessitates a 
water spray on the outside of the shell to cool 
it. Various devices have been designed to 
overcome this, such as the Brown Rotary 
Distributor, the Baker-Neuman, the Roe Dis- 
tributor, the Kennedy Top, the McKee Top, 
the Neeland Top, and others. 

These devices vary widely in the details of 
their construction and the principles on which 
they operate. Some rotate through a certain 
arc, thus dropping the charge at different 
segments of the circle; others use a cylindrical 
skip the bottom of which drops, allowing the 
charge to fall vertically upon the center of the 
bell, w^hile others have arrangements of baffle 
plates to deflect the stock as desired. How- 
ever, details of the many arrangements can 
hardly be discussed here. 

Openings — For the escape of the gases 
incident to the operation of the furnace, from 

27 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 




BAER EXPLOSION VALVE 



28 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 


one to four openings are provided, piercing the 
furnace top, and from these openings lead 
fire brick lined pipes termed the downcomer, or 
downtake, which in turn lead to the dust 
catcher. There are also often provided other 
openings closed by weighted doors, called 
explosion doors, which in case of a slip, give 
relief to the temporarily high pressure of gases. 
This construction is not generally used in the 
newer furnaces, where the top is made suffi- 
ciently heavy to withstand this excess pressure. 

The Baer Explosion Valve is said to have 
given excellent results. This type of valve 
may be set to raise at any desired pressure, 
affording gradual release. Where installed it 
has entirely overcome the troubles due to 
ejection of stock from the furnace top. 

From the top of the downcomer extend short 
vertical pipes called bleeders, which are closed 
with a valve at the top and thus allow the 
escape of gas into the air at any time this may 
be necessary. These are usually lined with 
from 2Y 2 " to 3" of fire brick. 

Piping — Downcomer — The diameter of 
the downcomer is dependent on the size of the 
furnace and volume of gas given off. It should 
be of such size, however, as to prevent a too 
rapid flow of gases, which occur with excessive 
top pressures. Such high pressures result in 
carrying an excess of dust and consequent 
wear on the brickwork, especially with the 

29 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 

modern tendency toward harder driving. It 
usually has a 9" fire brick lining. 

Dust Catcher — The object of the dust 
catcher, as its name implies, is to reduce as 
much as possible the amount of dust which 
shall be carried beyond it, this dust causing 
much trouble from clogging of the flues, stoves, 
boilers, etc. The principle of the operation of 
the dust catcher is merely that of the decreased 
velocity due to increasing the area of the con- 
ducting pipe, thus allowing the dust to settle. 
For this reason the greater the difference be- 
tween the diameters of the downcomer and the 
dust catcher, the greater the percentage of 
dust which will be deposited. 

The dust catcher is a large brick-lined 
vertical steel cylinder from 15' to 30' in diameter, 
usually with a dome or conical top and with an 
inverted conical bottom which has an opening 
through which the accumulated dust can be 
discharged. With the ordinary type of dust 
catcher, the flue dust in the gas can usually 
be reduced sufficiently to give satisfactory 
results in the stoves and under the boilers, but 
if the gas is to be used for gas engines, it must 
be subjected to further treatment in some 
type of gas washer. There are a number of 
these, including both stationary and centrifugal 
washers. 

Gas Mains — From the dust catcher or gas 
washers, as the case may be, the gas is piped 

30 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 

through the main directly to the stoves and to 
the boilers or gas engines, for fuel. This pipe 
usually has a 43^' r fire brick lining. 

The lining for the "cold side," as it is 
termed, i.e., the downcomer, dust catcher and 
gas main, is naturally not usually subject to as 
high temperatures as is the hot side, but there 
are times in nearly every furnace campaign 
when the top temperatures and consequently 
the temperatures in the cold side piping rise 
several hundred degrees above normal and it 
is merely the part of wisdom to be fully insured 
against trouble from this source by a brick 
lining amply refractory. 

In addition to the effect of the heat the 
brick are continuously subject to the rush of 
furnace gases laden with dust from the ore, 
coke and limestone and the abrasion is often- 
times very severe. An intelligent selection of 
suitable clays gives a brick very refractory but 
also dense and tough. 

Boiler Plant — The boiler plant to supply 
power for the blowing engines, lighting, pump- 
ing, hoisting, etc., differs in no important 
particulars from the ordinary power plant, 
save that it is usually so arranged as to operate 
with furnace gas as a fuel. It must also be 
adapted to use coal, should the furnace be out 
of blast, or not working properly, and its nor- 
mal fuel supply thus be unavailable. 

Blowing Engines — These engines supply- 
ing the blast for the furnace obviously form a 

31 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

most important portion of the furnace equip- 
ment but one which can hardly be considered 
in detail here. The engines are usually com- 
pound and are either vertical, horizontal or a 
combination of the two. The turbine blower 
is also being introduced. While until recently 
steam w^as in this country universally the mo- 
tive power, a number of the largest and most 
recent installations have been gas engines. 

The one thing which has retarded the 
earlier adoption of the gas engine operating 
with blast furnace gases has been the difficulty 
of economically and thoroughly washing the 
gases so as to give good and reliable results. 
This now seems to have been accomplished and 
in all probability future construction will see 
an increasingly large proportion of gas engine 
driven installations. 

Cold Blast Main — This is the main which 
conducts the blast from the engine to the 
stoves. 

HOT BLAST STOVES 

General Description — These stoves, so 
called, are for the heating of the blast previous 
to its introduction into the furnace, the heat 
being derived from the burning of the gases 
given off from the furnace during its operation. 

The first stoves in use were of cast-iron. 
The gases were burned around and circulated 
among U-shaped cast-iron pipes enclosed in a 
fire brick structure; the blast in turn passing 

32 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

through these tubes, picked up considerable 
heat. This process was continuous — a re- 
cuperative process. However, it was subject 
to a number of defects among which was the 
burning out of the tubes, making it impossible 
to obtain more than 900° F. in the blast. This 
type of stove was followed by the fire brick 
stove operated on the regenerative principle 
and by its use a hot blast temperature of 
approximately 1500° F. can be obtained. 

The outside steel shell, some 18' to 22' in 
diameter and 80' to 100', and in some cases 
even 130' high, encloses a structure of fire 
brick which consists essentially of two parts, 
i.e., the combustion chamber and the checker 
work. This combustion chamber is an open 
vertical shaft extending from the bottom 
to the top of the stove. The gas is introduced 
at the bottom, together with a suitable supply 
of air through air valves, to give proper 
combustion. The gas burns, developing a high 
temperature, and the escaping products of 
combustion passing up the combustion chamber 
and then down through this series of regular 
parallel flues called " checker work," give off 
the major portion of their heat to the brick- 
work and then escape through the stack or 
chimney. The checker work may be so di- 
vided as to have one, two, three or even more 
passes before the gases escape to the outer air, 

33 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

the number of these dependent on the type 
of stove. 

The mass of brickwork having attained a 
high temperature, the valves are reversed and 
the blast from the engine is driven through the 
stoves in a reversed direction, and in passing 
over the heated brickwork, is raised to possibly 
1300° or 1400° F. This blast is kept on until 
the temperature, naturally falling as the stove 
cools, is reduced to 1100° or 1200° F. when the 
stove is put on gas and allowed to store up a 
further supply of heat. However, it must not 
be inferred that the temperature of the blast 
as it issues from the tuyeres is normally allowed 
to vary by any such amount. Such a variation 
would have too great an effect in changing 
the height of the zone of fusion and would 
result in very irregular running. 

The usual method is to keep the temperature 
of the blast proper as nearly constant as possible. 
This is effected by opening the valve in the 
mixer pipe, as it is called, allowing cold air 
to mingle with the air from the stove, then, 
as the stove gradually cools, the valve is more 
nearly closed and the blast is finally at the 
temperature attained from the checkers of the 
stoves. 

In this way the air from a stove may be at, 
say 1300° F. when first put on the furnace, 
the mixer valve opened sufficiently that the 

34 



Harbisox-Walker Refractories Co., Pittsburgh, Pa. 

temperature of the air at the tuyeres be only 
1100° F. but this latter temperature will be 
maintained for a full hour in spite of the drop 
in the stove, by the gradual changing of the 
valve in the mixer and consequent decrease 
in the amount of cold air admitted. 

By this method of operating, a practically 
constant temperature is maintained. If a 
stove is comparatively new and in good con- 
dition, it should hold its temperature with a 
drop of not more than 100° to 175° F. in an 
hour. If the brick have become vitrified, how- 
ever, or the stoves are dirty, it will not hold 
up as w^ell. 

It is usual to have four stoves, so that while 
one is in blast the other three may be on gas. 
With such arrangement it is customary to have 
a stove in blast about one hour, while with 
four stoves, it has three hours in which to 
become hot. In some of the newer installations 
five stoves are installed, so that the full com- 
plement may be available while the cleaning 
of one stove is in progress. 

There are few important locations where 
fire brick are used that have had less real 
study and intelligent consideration by the user 
than in the hot blast stove. 

Those men who are giving the matter most 
thought and on whom rests the burden of 
responsibility for economical furnace operation, 

35 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 

are advocating the use of the highest grade 
stove brick obtainable. The use of first quality 
brick, not only through the first pass and well 
into the second pass of stoves, but even to 
within a short distance of the stove bottom, is 
advocated by many. 

The lack of proper attention to the import- 
ance of quality in stove brick has undoubtedly 
been due to insufficient data regarding the 
actual performance of various qualities of brick 
in the stoves. Furthermore, there is the usual 
temptation to accept the very considerable 
saving in first cost in so large an item as fire 
brick for large stove installations wdien the 
consequences of such a decision can be put 
forward into that indefinite but very positive 
future when all basic shortcomings in construc- 
tion become apparent. 

In the selection of a brick, what is of vital 
importance is not what is paid per thousand 
brick but what is actually paid per thousand 
heat units. The office of the brick is to take 
on and give off heat units and how well it 
performs this test depends strictly upon the 
maintenance of its thermal capacity. Two 
brick may show up equally well in a straight 
heat test, yet the one, after a few months of 
hard usage, becomes vitrified, its thermal 
capacity lowered, while the other is practically 
unaffected and will continue to perform its 
work for years. It is safe to say that the day 

36 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

is coming when the factor of efficiency in stove 
refractories will be appreciated more nearly 
at its worth and the blast furnace manager 
will not permit himself to be handicapped by 
inefficient equipment. 

In general, stoves are divided into two 
classes, the side combustion and centre com- 
bustion, types of which are shown on pages 
38 to 51, inclusive. 

There may be a stack for each stove, or 
one only for the whole group. This is some- 
times placed at the end of the line of stoves, 
but w T hen so placed, tends naturally to favor 
the stoves nearest it, and for this reason is 
more often about midway in the group. In 
certain types of stoves, such for instance as 
that shown on page 42, a chimney, is provided 
for each at the top of the stoves. Chimneys 
or stacks are all provided with fire brick linings. 

Valves — The valves to be considered 
consist of the cold blast valve, hot blast valve, 
air valve, gas valve and chimney valve. The 
cold blast and air valves admit air only at 
atmospheric temperature or slightly above it 
as the air comes from the engine. Some 
ordinary form of gate valve is here satisfactory. 
The gas valve admits gas at furnace top 
temperatures, i.e., 400° to 600° F. except as 
it is cooled by radiation. It is not usually 
water-cooled. The temperature to which the 
chimney valve is subjected is dependent upon 

37 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 



CLEAN-OUT 
~ DOOR 




HOT BLAST MAIN 



SECTION A-A AIR INLET 

CALDER HOT BLAST STOVE 
The S. R. Smythe Co., Engineers, Pittsburgh, pa. 



3S 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 




section b-b 

CLEAN-OUTDOOR ^= : 5======s==== :i ^ " ^AIR INLET 

note: 

MADE OF 9 £.I3> 2 BRICK 

calder hot blast stove 

The S. R. Smythe Co., Engineers, Pittsburgh, pa. 



39 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 




FOOTE PATENT STOVE 
D. Lamond & Son, Engineers, Pittsburgh, pa. 



40 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 




ENLARGED CROSS SECTION 



CHECKER BRICK 



FOOTE PATENT STOVE 
D. Lamond & Son, Engineers, Pittsburgh, pa. 



41 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 




SECTIONAL ELEVATION 

McCLURE STOVE 
W. McClure, Son & Co., Engineers, Pittsburgh, pa. 



42 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 




McCLURE STOVE 
G. W. McClure, Son & Co., Engineers, Pittsburgh, pa. 



43 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 




NELSON STOVE 
Arthur G. McKee, Engineer, Cleveland, o. 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 




NELSON STOVE 

Arthur G. McKee, Engineer, Cleveland o. 



45 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 



PLATFORM LEVEL 




22 IS. DIA 



ROBERTS PATENT STOVE 
F. C. Roberts & Co., Engineers, Philadelphia, pa. 



46 



Harbisox-Walker Refractories Co., Pittsburgh. Pa. 



HALF SECTION ON I -J 




HALF SECTION ON 6-H 




ROBERTS PATENT STOVE 
F. C. Roberts & Co., Engineers, Philadelphia, pa. 



47 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 



E. LEV. TOP OF PLATFORM 




JULIAN KENNEDY STOVE 
Julian Kennedy, Engineer, Pittsburgh, pa. 



4S 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 




JULIAN KENNEDY STOVE 
Julian Kennedy, Engineer, Pittsburgh, pa. 



49 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 




WHITE & KERNAN HOT BLAST STOVE 
F. L. White, Pittsburgh, pa. 



50 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 




WHITE & KERN AN HOT BLAST STOVE 
F. L. White, Pittsburgh, pa. 



51 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

the temperature of the outgoing gas from the 
stove and may be as high as 900° or 1000° F. 
although this is by no means usually the case, 
and shows that a large amount of heat is 
wasted, being unabsorbed by the checker brick. 
This valve may or may not be water-cooled 
and may be one of several types. 

The hot blast valve must withstand often 
some 1500° F. and is also usually of the mush- 
room type, water-cooled, with its seat so 
arranged as to be easily renewable, and is lined 
throughout with a high grade of fire brick. 
It is subjected to by far greater wear than are 
the other valves. 

In order that the blast may be taken off 
the furnace without stopping the engines, a 
valve termed the snort valve is usually intro- 
duced in the cold blast main and is operated 
from the cast house. 

DISPOSAL EQUIPMENT 

Pig Beds — The previous description of 
equipment has been that for the production 
of the pig iron and its accompanying slag. 
The following equipment is that applicable 
to its disposition. 

As the metal is tapped from the furnace, 
it is allowed to flow through a channel in the 
sandy bed of the cast house into the so-called 
"pig beds," or through runners into ladles. 
It is apparent that if the iron is to be used in 
making steel in a nearby open hearth or bessemer 

52 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

plant, there is a marked saving in using the 
hot metal thus saving the re-melting costs. 
In such cases the molten iron is merely allowed 
to run off into a ladle car placed below the level 
of the cast house floor and then conveyed to 
the Bessemer converter or the open hearth 
furnace. 

As the iron is tapped from the furnace, 
the first portion is usually comparatively free 
from slag, but later as the hearth is nearly 
emptied, slag mingles with it and it is neces- 
sary to separate the two. The old method 
was by molding a dam in the runner or trough 
leading from the tapping hole to the casting beds 
and between this dam and the furnace to suspend 
an iron plate or skimmer across the trough, the 
bottom of the skimmer being lower than the 
top of the dam. This effectually intercepts the 
slag, which is led off at one side. Present 
practice is to use a heavy cast iron trough of 
practically identical form with the molded 
sand dam. With the casting, much less skill 
is required and its use is considerably more 
satisfactory. 

When the metal is to be cast into pigs 
in pig beds, the iron is directed along a de- 
pression or runner in the sand bed of the cast 
house, from which it flows into cross-runners, 
thence into the pig molds. 

The pig molds are usually made in the 
molding sand of the floor with wooden patterns 

53 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

and must be re-made after each cast. In 
some cases instead of being cast in the form of 
pigs, the number of cross-runners is greatly 
increased so that the iron is led into a series 
of long parallel "sows" as the metal in the 
cross-runner is often termed. These sows are 
then broken into the lengths of ordinary pig, 
either by hand or some form of machine breaker. 

Chills — There is a disadvantage in such 
sand cast pig where it is to be used in the basic 
open hearth, due to the greater or less quantity 
of adherent sand which being highly silicious, 
makes with the necessary lime to flux it, a 
heavy slag. For this reason primarily the iron 
is sometimes cast in what are termed "chills." 
These are merely cast-iron pig molds', into 
which the metal is led, just as though casting 
in sand. Inasmuch as the only preparation 
of the molds is a washing with a clay grout 
or lime to prevent adherence of iron, a larger 
tonnage can be handled in a cast house of 
given floor space with chills than when sand 
cast. 

Casting Machine — With the increased 
size and output of modern furnaces, it is im- 
possible to handle the enormous product as 
outlined above. This has led to the develop- 
ment of the pig casting machine where the 
casting is done from a ladle. Of the two types 
of machine the more modern and satisfactory 
consists of an endless chain carrying a series 

54 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

of steel or cast iron molds parallel to each 
other with the edges overlapping. As the ladle 
is tipped, the travel of the chain brings into 
position a continuous train of empty molds 
to be filled. The chain carries the full molds 
through a trough of water, thus cooling the 
iron so that it may be dumped at the turn 
into cars, ready to be shipped, and on the return 
the mold is sprayed with lime or given other 
coating to prevent the metal sticking. There 
are a number of modifications to the above. 

The other and older type of machine carries 
the series of molds on the periphery of a 
horizontal revolving wheel some 35' to 40' in 
diameter, but the upkeep of this type has 
apparently prcven more expensive than that 
in which the endless chain is used. 

Slag Disposal — Although a vast amount 
of research has been and is being conducted 
relative to economical and if possible, profitable 
uses for slag, by far the larger portion of it 
is as yet thrown aw^ay, the only problem being 
one of the cheapest disposition. It is usually 
allowed to flow into slag cars which are shaped 
somewhat like a thimble, often lined with fire 
brick, and the slag is then hauled to the dump 
and emptied while still molten. In many of 
the older plants there are yet in use small iron 
slag cars with a rectangular body in w T hich the 
slag is allowed to cool, the blocks of slag being 
then dumped. Comparatively recently many 

55 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

furnaces have installed equipment for the gran- 
ulation of slag which, on being tapped from the 
furnace, is allowed to flow into a large masonry 
tank of water, or direct into steel cars with a 
jet of water playing under the slag as it falls 
from the runner. In this way it is broken up 
into particles similar to very coarse sand, and 
can then be handled from the tank to cars 
by some form of bucket and used as ballast or 
filling for which it is very satisfactory. This 
method also has the merit of cheapness. The 
manufacture of brick from blast furnace slag 
has been attempted in numberless instances, 
but these experiments have been successful in 
only a few instances with slag occurring in 
American practice. Failure is chiefly due to 
the slaking of the lime content on continued 
exposure to atmospheric conditions. The large 
and increasing use of certain blast furnace slags 
in the manufacture of Portland cement bids 
fair to make slag one of the most important 
by-products of the iron and steel industry. 
It also finds a somewhat limited use as a sub- 
stitute for roofing gravel, etc. 



56 




->1ATE RIALS -ORES 



CHAPTER II 

T is difficult to frame a definition which 
shall be absolutely accurate from all 
points of view, and furthermore, usage 
has much to do with the various terms 
employed, but in general iron ore is a compound 
of iron combined w^ith certain elements. This 
compound is more or less intimately mixed with 
earthy impurities or gangue as it is called. In 
order to be an ore in the sense here used, the 
iron must be in sufficient quantities and in 
combination with such elements as shall permit 
its smelting on a commercially profitable basis. 

Although iron is one of the most widely 
distributed of the elements, it practically never 
occurs native or in the form of pure metallic 
iron, so great is its affinity for other elements. 
In general, the compounds of iron available 
for the blast furnace are the oxides, which 
include the three groups, the Hematites, the 
Brown Ores, and the Magnetites, these com- 



57 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

prising more than 99% of the ore produced in 
this country, and the Carbonates, less than 1%. 

The above are given in the order of their 
importance. 

There is also the general division of all ores 
into two classes, i.e., Bessemer and non- 
Bessemer or basic, dependent upon the content 
of phosphorus. This terminology comes from 
the fact that in the acid Bessemer method of 
making steel, no phosphorus is removed during 
the process. Hence, the pig iron from which 
the steel is made must have no greater quantity 
of phosphorus than will maintain the Bessemer 
limit, .1% phosphorus in the steel. Practically 
all the phosphorus in the ore goes into the pig 
iron. This usually means that a Bessemer ore 
must contain no more than .045% to .05% 
phosphorus, the limit being .001% phosphorus 
for each per cent, of iron in the ore. Bessemer 
and non-Bessemer ores are in turn separated 
into other groups, depending upon their phos- 
phorus content, but the two general divisions 
are as cited. 

Hematites — These ores, often termed 
"Red Hematites," are anhydrous sesquioxides, 
Fe2 03, identical in composition with ordinary 
red iron rust, and if pure and without the 
gangue, would analyze 70% iron. They com- 
prised during the year 1908 more than 88% 
of the total ore mined in this country. They 
give the characteristic red streak on porcelain. 

58 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 

The formation, as in the case of a majority 
of the iron ores, varies widely from a massive 
formation so hard that it can with difficulty 
be drilled and blasted, to the earthy, loamy 
formations which can be easily handled in 
open cut with the steam shovel. One of its 
forms is the familiar crystalline ore termed 
Specular Hematite, much used in open hearth 
practice; another, the Foliated form, often 
called Micaceous ore. In accordance with its 
various formations it may be locally known as 
Gray ore, Fossil ore, or Oolitic ore, etc. It is 
but very slightly attracted to the magnet. 
The range of composition in the Lake Superior 
district, by far the largest producer, is given 
for the year 1907, as follows: 





Per Cent. 




Per Cent 


Fe 


39.0 


to 


67.0 


Si0 2 


1.0 


to 


43.0 


P 


.01 


to 


1.0 


S 


.005 


to 


.14 


Mn 


.03 


to 


8.7 



They occur both as Bessemer and non-Bessemer 
ores. 

They occur as is shown on the map, (w^hich 
is attached to the inner back cover), principally 
in northern Minnesota, the northern peninsula 
of Michigan, northern Wisconsin, Alabama and 
Tennessee. The so-called Lake Superior district 
in the northern part of Minnesota, Michigan 

59 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 

and Wisconsin supplies over 90% of the total 
Hematite ores produced. 

There are here five great ranges, in order of 
their importance being Mesabi, Menominee, 
Marquette, Gogebic and Vermillion, the product 
of the last four being termed "old range" ores, 
to distinguish them from the Mesabi. As of 
interest, their relative tonnage for the last 
four years is shown: 

1907 1908 

Long Tons Long Tons 

Mesabi 27,495,708 17,257,350 

Menominee... 4,964,728 2,679,156 

Marquette. . . . 4,388,073 2,414,632 

Gogebic 3,637,102 2,699,856 

Vermillion.... 1,685,267 841,544 

Miscellaneous. 95,790 122,449 

42,266,668 26,014,987 

1909 1910 



Mesabi. . . . 
Menominee 
Marquette. 
Gogebic . . . 
Vermillion . 
Miscellaneous 



Long Tons Long Tons 

28,176,281 29,201,760 

4,875,385 4,237,738 

4,256,172 4,392,726 

4,088,057 4,315,314 

1,108,215 1,203,177 

82,757 91,682 



42,586,869 43,442,397 

The Mesabi ores are worthy of special note, 

both on account of their quantity and the effect 

that their use has had upon blast furnace 

practice. This is due to their formation, as 

60 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

these ores are practically all of a loamy texture 
and of extreme fineness. 

Brown Ores — These are hydrous sesquiox- 
ides of iron and are distinguished from the true 
Hematites only by the presence of their water 
of combination. Approximately 7% of the 
total ore produced in 1908 belonged to this 
class. They are represented by the formula, 
Fe2 03nH2 0, and if pure would contain from 
59.8% to 66% of iron, this amount depending 
on the degree of hydration. There are, as in 
the case of the Hematites, many varieties, 
Limonite being one of the most important 
ones, 2 Fe2 03 3 H 2 0, and according to such 
formations, are locally known as Brown ores. 
Bog ores, Brown Hematites, Limonites, etc. 
If heated to sufficient temperature to expel the 
water of combination they change to true 
Hematites. In accordance with the degree of 
their hydration, the characteristic streak varies 
from yellow through brown to red. 

Their formation is often massive but also 
occurs as concretionary, as veins in quartz 
or in pocket formation in residual clay deposits. 
Their occurrence is remarkably persistent 
throughout the entire eastern part of the 
Appalachian region, extending from New Eng- 
land to Alabama. A reference to the tables 
on pages 65, 66 and 67 will show Alabama, 
Virginia, Tennessee and Georgia to be by far the 
heaviest producers. 

61 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

This formation as a whole is naturally- 
separated into the two divisions of the Moun- 
tain and Valley Brown ores, and the Oriskany 
Brown ores of Alleghany County, Virginia, 
and Central Pennsylvania. The Mountain and 
Valley ores, although persistent, show no 
deposits of great size and are very irregularly 
scattered; the Oriskany ore, on the other hand, 
although of about the same grade, occurs in 
much larger deposits in well defined strata 
sometimes several miles in length and of very 
considerable thickness. This form of occur- 
rence is important from the standpoint of 
production. 

Due to the phosphorus present, practically 
all the Brown ores are of non-Bessemer grade, 
the average range of analysis being: 

Average Range Average Range Average Range 

in Composition in Composition in Composition 

o f Mountain of Valley Ore. of O r i s k a n y 

Ore. Brown Ore. 

Fe 35.00-50.00 40.00-56.00 37.00-50.00 

Si0 2 10.00-30.00 5.00-20.00 10.00-25.00 

P .10- 2.00 .05- .50 .06- .50 

Mn .50-10.00 .30- 2.00 .50- 4.00 

Magnetites — The Magnetites, 
Fes04, comprise about 40% of the ore mined. 
It is the richest of the ores, having 72.4% iron 
when pure. It is very hard, heavy and dense, 
usually black or iron gray in color, of crystalline 
structure and possessed of marked magnetic 
properties, being nearly as magnetic as iron 
itself. This characteristic is all important if 

62 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

its concentration is necessary, a condition later 
to be taken up. It often carries with it large 
percentages of Titanium, the Adirondack region 
being the heaviest producer of both non- 
Titaniferous and Titaniferous ores, the latter 
varying from a high grade, low phosphorous 
ore through the Bessemer grades into the non- 
Bessemer. Due to its crystalline formation 
and magnetic properties, many varieties lend 
themselves to concentration with comparative 
ease, and may so be changed from non-Bessemer 
as mined, to Bessemer, or low phosphorous 
ores, by reason of the removal of apatite, the 
phosphorous-bearing mineral. 

Northern New Jersey is also a large producer, 
and southeastern Pennsylvania, near the vicinity 
of Cornwall, has most important mines, from 
which over twenty million tons have been taken. 
This latter formation is a peculiar one, as the 
Magnetite here occurs both in large and small 
masses, usually enclosed by sedimentary rocks 
instead of in igneous formations, as is generally 
the case. It is characterized by low phosphorus 
but is so high in sulphur, due to the presence 
of copper pyrites, as to require roasting. The 
presence of copper also produces a considerable 
percentage of this element in all pig iron made. 

In Page County, Virginia, and in North 
Carolina occur Magnetites which are of Bessemer 
quality. 

63 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 

Carbonates — The Carbonates, FeC0 3 , 
yielding 48.2% iron, if pure, are least important 
economically, forming less than 1% of the ore 
mined. The varieties are variously known lo- 
cally as Spathic ore, from the similarity in 
cleavage to feldspar, Kidney ore, Black Band 
ore, when associated with bituminous matter 
in coal veins, clay Iron-stone ore, from its 
frequent occurrence in beds of shale or clay, 
and as siderite, etc. 

Due to their low content of iron and high per- 
centage of carbon dioxide, which usually neces- 
sitates calcination before the ore is introduced 
into the furnace, Carbonates are of those least 
valuable. However, their association in occur- 
rence with coal veins and the fact that their 
gangue is often self-fluxing, in a measure off- 
sets the leanness of the ore. They are at 
present produced only in one state — Ohio. 

In general, the Magnetites are geologically 
the oldest of the ores and of an entirely different 
formation from the rest, being metamorphic. 
The Hematites are supposed to be the results 
of alteration of the Limonites, the primitive 
ores, by the heat and pressure of the earth's 
crust. 

The Carbonate ores are of still another for- 
mation, although on weathering, they may 
change to Limonites, on losing their CO2. 

As a general summary, the tables showing 
the ore production both by states and by varieties 
will be of interest. 

64 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 



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Harbison-Walker Refractories Co., Pittsburgh, Pa. 



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67 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

The total imports and exports in long tons 
for the years noted are also shown indicating 
the bearing foreign ores have upon our pro- 
duction. 

1907 1908 

Imports 1,229,168 776,898 

Exports 278,208 309,099 

1909 1910 

Imports 1,694,957 2,591,031 
Exports 455,934 644,875 

Items Affecting Valuation of Ores — 
The value of an ore is dependent upon its 
richness in iron, its composition, i.e., the minerals 
associated with it, and its location, as well as 
its physical condition, and it is impossible to 
consider any one of these qualifications entirely 
apart from the others, so interdependent are 
they. 

For instance, a very lean ore, one low in 
iron, may have considerable value due to the 
self-fluxing character of its gangue, and con- 
sequent low cost of smelting. On the other 
hand, a rich ore may have associated with the 
iron, elements so deleterious in effect upon the 
pig iron as to render it valueless without some 
method of removal of the impurities before 
smelting, which removal may be so costly as 
to render the ore unavailable. 

In general, ores profitable to smelt w^ill 
contain from as low as 30%, to as high as 60% 
or 65% metallic iron, in valuation each per 
cent, being termed a unit; thus, an ore with 

63 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

50% metallic iron will have 50 units. It is 
evident that since iron is the thing of value, 
in any given ore it must be in such quantity 
as to bear not only the cost of the ore laid down 
at the furnace, but the cost of its extraction 
with profit. Furthermore, as the cost of re- 
duction and melting any given quantity of iron 
as such, is constant, the variable enters in the 
disposition of the gangue. 

From this it will be seen that the value of 
an ore increases not in proportion to the in- 
crease in the number of units of iron, but very 
much faster, as there is a corresponding de- 
crease in the gangue to be handled. 

As a whole, the gangue of iron ores consists 
principally of silica and alumina, together with 
small amounts of lime, magnesia and oxides 
of manganese and the alkalies, as well as more 
or less phosphorus and sulphur. So far as 
affecting the quality of the pig iron produced, 
the exact percentages of all the above, with 
the exception of sulphur, manganese and 
phosphorus are of little importance, as they are 
easily controlled by the burdening and operation 
of the furnace. 

The sulphur, however, is but partly under 
control and requires for its even partial removal 
in the furnace, additional flux and fuel. Al- 
though no exact percentages can be given, as 
it is dependent on the analysis of the particular 
ore, the furnace operation, etc., any ore having 
more than .50% to .75% sulphur must be treated 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 

to remove a portion before being charged. 
Such cost, together with the added expense of 
its smelting, will then determine whether or not 
the ore is available for even such pig iron 
specifications as allow comparatively high sul- 
phur. It might still be used in a mix with low 
sulphur ore. 

Marganese is another element but partially 
under control. It is not harmful to pig iron 
within the limits of, say 1% for Bessemer iron 
and 23^% for the Open Hearth. On the 
average, about three-fourths of the manganese 
in the ore will be reduced. However, if the 
manganese is sufficiently high to be, say, 18% 
to 20% or over in the pig, the ore then becomes 
suitable for the manufacture of speigeleisen, and 
with proper burdening, for the manufacture of 
standard ferro-manganese. 

In phosphorus we have, more than in any 
other element, the controlling factor determining 
whether an ore is available from the standpoint 
of composition, and if so, what its classification. 
It must be assumed that practically all the 
phosphorus in the ore goes into the iron, as 
very little if any, can be eliminated in the blast 
furnace. This percentage of phosphorus leads 
to the two general divisions of Bessemer and 
non-Bessemer ores previously referred to. 

Location — The location of ore bodies is 
naturally a most important consideration. Their 

70 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

location as regards fuel supply, means of trans- 
portation, and distance from the market, are 
among the determining factors. The size of 
the deposits will determine whether there is 
justification for the erection of a plant, although 
the wisdom of such an outlay will depend, in 
turn, wholly on the location of the present or 
future market for the output of the plant. 

Mining costs, while low at the surface, are 
subject to advance as the work proceeds; in 
a shaft operation, the increased haul and 
difficulty of taking care of the water add their 
quota of expense; in a stripping proposition, 
the increasing over-burden as the ore strata 
dip means increased costs. 

There also must be considered the natural 
exhaustion of the richer and more accessible 
deposits, tending each year to bring into effective 
competition ores of lower grades. All these 
items, as well as the character of the entire ore 
formation, are a few of the factors entering into 
the problem. 

TREATMENT OF ORES 

Although but a comparatively small pro- 
portion of the ores in this country require 
preliminary treatment before their introduc- 
tion into the blast furnace, it is with certain 
classes advisable. The treatment usually comes 
under one of four heads: — roasting, calcining, 
concentration and nodulizing. 

Roasting — The object of roasting is the 
removal of sulphur and consists in heating the 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

ore in contact with air to as high a temperature 
as possible without incipient fusion. The sul- 
phur usually exists in the form of iron pyrites, 
FeS2, one atom of which is very easily expelled 
on heating either with or without contact with 
air, as expressed in the equation FeS2 = 
FeS + S. To drive off the remaining sulphur, 
not only must there be sufficient heat, but an 
excess of air. This takes place in two stages: 

FeS + 2 2 = FeS0 4 
2FeS0 4 = Fe 2 3 + 2S0 2 + O. 

In this way the sulphur may be reduced to 
but a trace of the original quantity present. 

This operation may be carried on either in 
open heaps, in stalls or in kilns. The last is 
most economical and the temperature is under 
better control. Roasting in heaps is still 
practiced where fuel is cheap and there is ample 
space. A layer of coal a few inches in thickness 
is first spread on the ground, then a layer of 
ore, then coal, and so on, until a mass several 
feet in thickness is built up. The bottom is 
ignited and the whole heap slowly roasts. As 
an aid to the draft, the coarser ore is sometimes 
built into the bottom of the heap in channels. 
The heat may also be controlled in a great 
measure by the shape of the heap, whether deep 
and wide, or in comparatively long and narrow 
masses. Draft through the mass is controlled 
by the application of fine ore at any place where 
combustion seems to be too active. 

72 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

A disadvantage is that certain portions of 
the heap may be insufficiently roasted while 
others where the draft is less impeded, due to 
coarser ore, etc., may easily get so hot as to 
fuse the surface of the ore and thus prevent 
thorough roasting. 

Stalls, as their name indicates, are merely 
rectangular spaces enclosed on three sides by 
walls 8' to 10' high, through the bottom of 
which are holes for the draft. The ore is piled 
in these in much the same manner as in heap 
roasting. The^ defects of the latter method are 
present here, but not to so great an extent, as 
combustion is under somewhat better control. 

In kiln roasting, a number of different types 
of kilns are used. One is the Gjers kiln, q 
vertical steel shell with a diameter of 15' to 25' 
and lined with 13^" to 18" of fire brick. The 
height varies with the diameter, ranging from 
15' to 35', and the shell is somewhat contracted 
at the bottom, having holes for the admission 
of air and withdrawal of ore. The ore is mixed 
with coal and the kiln burns continuously, 
fresh charges being inserted at the top as the 
roasted ore is withdrawn from the bottom. 

In a recent type of the Davis-Colby kiln, 
the ore descends in the form of a comparatively 
thin sheet, running the length of a rectangular 
kiln between two parallel flues of fire brick. 
These outer flues in which combustion occurs 
are fed by gas burners. The products of 

73 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 




WEDGE MECHANICAL FURNACE 
Wedge Mechanical Furnace Co., 
greenwich point, philadelphia, pa. 



74 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 

combustion penetrate the descending body of 
ore through many openings and enter the inner 
flue, from this going to the stack. Either 
liquid or gaseous fuel may be used. 

The illustration on page 74 shows another 
type of furnace — the Wedge Mechanical Fur- 
nace, which is built in various types, adapting 
it to the magnetic roasting and the desul- 
phurizing of iron ores, as well as roasting of 
various ores and materials. The important 
points to be noted in the Wedge Furnace are 
uniform control of temperatures, protection of 
metal parts by brick (the 4' diameter hollow 
central shaft being covered with tile attached 
to and revolving with the shaft), no loss of 
heat in making repairs, and low cost of operation 
and maintenance. 

Calcining — This is usually done with the 
object of making hard, dense ores, more perme- 
able to the action of gases in the furnace, of 
removing the CO2 from the carbonate ores, 
of rendering a non-magnetic ore magnetic as a 
preliminary to further concentration, or of 
expelling the water that may be present. 

With certain ores, particularly the Mag- 
netites, carrying silicates of iron in the gangue, 
this silicate is oxidized on calcination and the ore 
tends to become disintegrated. In many cases 
with other gangue material the ores are rendered 
more porous allowing freer access to the furnace 
gases. Continued application of a low red 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

heat to Magnetite, Fe 3 0.i also changes it to 
the form of Fe 2 3 , considerably more sus- 
ceptible to reduction in the furnace, and cal- 
cination is employed in some instances with 
this object. 

In the case of Carbonates, the equation on 
calcination with access of the air is: 

2 FeC0 3 + O - Fe 2 3 + 2C0 2 

In considering the calcination of the Hem- 
atites in order to render them magnetic, two 
methods may be employed. They may either 
be heated strongly in a neutral atmosphere 
with the result: 

3 Fe 2 3 = 2 Fe 3 4 + O, 

or, 
3 Fe 2 3 = Fe 6 7 +2 0. 
Either of these oxides are strictly magnetic. 
The disadvantage of this method is that such 
high heats must be employed as to incur danger 
of fusion of the ore. They may also be heated 
at a comparatively moderate temperature in 
the presence of a reducing agent such as coal, 
or reducing gases occurring, for instance, in 
producer gas. In this method the ordinary 
type of vertical shaft kiln is usually available. 

Brown ores, on application of sufficient heat, 
lose their water of combination and then become 
true Hematites and may be treated as such. 

Carbonates, although changing to Fe 2 3 on 
heating, with access of air, may yet be reduced 

76 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

to the magnetic form by heating without access 
of air, the following equation occurring: 

6 FeC0 3 = Fe 6 7 + 5 C0 2 + CO 

There is little occasion for such treatment, 
as Carbonates are of small importance as com- 
pared with the other ores. 

Concentration — Concentration, as its 
name implies, always results in a richer ore, 
but its object may also be the removal of certain 
objectionable materials. Many of the ores 
which it is necessary to concentrate are of them- 
selves far richer than others profitably smelted 
without concentration, but they are too high 
in certain elements or minerals, such as phos- 
phorus, titanium, etc., which it is necessary to 
extract before they can be profitably handled. 

Concentration usually takes the form of 
washing, jigging or magnetic concentration, 
the latter either wet or dry. Washing is applic- 
able to the clayey ores and is conducted in one 
of the various types of washers in which the 
whole mass of ore is constantly stirred as it 
progresses through the washer, and running 
water carries off the clay, leaving the heavier 
ore. 

In jigging, applicable to sandy or pebbly 
ores, the material is placed in boxes with 
perforated bottoms. These in turn are in 
tanks of water, and the constant jarring of the 
jig then agitates the material in the box and 

77 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 

allows it to settle in layers in accordance with 
its specific gravity; the ore goes to the bottom, 
while the pebbles and sand are allowed to waste 
as they accumulate and overflow. 

Magnetic separation, whether wet or dry, 
depends upon the difference in magnetic perme- 
ability between certain minerals in the gangue 
of the ore and the magnetic oxide itself. It is, 
of course, immaterial whether the ore was 
originally magnetic or made so by subsequent 
treatment. The ore is crushed to suitable 
fineness and then subjected to the influence 
of magnets as it passes in a thin layer before 
them. This effects more or less separation. 
The magnetic portion of the stream is, in certain 
forms of separator, carried by a belt until it 
is out of the magnetic field, then allowed to 
drop into bins, while the portions which are 
unaffected by the magnets merely go to the 
tailings. 

Separation by this method is essentially 
a grinding proposition, and it is in the grinding 
and screening that there is the larger portion 
of the costs, for the actual separation when 
once ground is comparatively inexpensive. 
The fact that such grinding separates the 
magnetic ore from the gangue is due to the 
crystalline formation, and the relative fineness 
to which any ore must be ground is in a great 
measure dependent on the structure of such 
ore, and the relative formation of the various 

78 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

minerals as they are combined in this crystalli- 
zation. The many details in connection with 
such separation, such as the suitable fineness 
of the ore and the type of separator adapted 
to it, are problems to be solved for each in- 
dividual ore. 

Wet separation is employed rather more 
abroad than in this country, and is a necessity 
with certain types of ore, where they must be 
ground to an almost impalpable powder. The 
principles involved are the same as in dry 
separation except that they are carried on with 
the ores mingled with water. 

In general, this form of concentration finds 
a most useful application in the reduction of 
the phosphorus in Magnetites, and also in the 
reduction of the titanium. It bids fair to make 
available enormous deposits in New York 
which have hitherto been impossible to smelt 
profitably, due to the refractory nature of 
titanium-bearing oxides. 

In typical ores the iron may be raised from 
60% in the ore to 67% or even higher in the 
concentrates, and the phosphorus reduced from, 
say 1.75% to less than .70%, the tailings of 
apatite from such separation forming a valuable 
by-product. Such a statement, however, is 
of little value as the treatment of each ore 
forms a problem by itself, and one which can be 
solved only by actual tests. 

79 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

Nodulizing — The necessity for nodulizing 
is brought about by the difficulty of smelting 
very fine ores, either occurring naturally in 
such condition or made so by the processes of 
concentration. If very fine, the ore is easily 
blown about by the blast, and a very consider- 
able percentage is carried away through the 
downcomers and distributed through the flues 
of the furnace plant. 

The ideal ore should be uniformly lumpy, 
neither too fine nor coarse. Where both fine 
and lumpy ores are used, the tendency of the 
fines is to fill the voids of the coarser ore, pro- 
ducing a comparatively compact mass difficult 
for the gases to penetrate, and in a number of 
other ways causing furnace troubles. 

This has led to a treatment of certain fine 
ores in nodulizing kilns which, in type, are 
nothing more or less than cement kilns. 

The nodulizing kiln consists of an almost 
horizontal cylindrical steel shell approximately 
100' in length and possibly 8' in diameter, 
lined w T ith a high grade fire brick, this high 
grade material being especially necessary at 
the hot or discharge end. The kiln is placed 
at a slight angle with the horizontal and rotates 
during its operation so that the charge is con- 
tinually working toward the lower end. At 
this discharge end a pipe is introduced convey- 
ing powdered coal which is ignited, giving 
intense heat, and the feed end of the kiln 

80 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

is connected with a stack giving sufficient 
draft. The lining is usually 9" to 12 " thick at 
the discharge end and from 4j^ r/ to 9" at the feed 
end. 

The problem of the best brick for this work 
is one well worth the attention of the operator. 
It must, of course, be highly refractory and 
at the same time resist abrasive action. If too 
dense, it fails to properly take the coating of 
clinker and tends to spawl away in chunks as 
the kiln cools. If insufficiently refractory, it 
rapidly melts under the intense heats. It is 
also all important that the shapes used in the 
lining be well made in order to fit tightly against 
the shell, as the continuous rotation of the kiln 
will jar loose any lining improperly made or 
placed. 

At the feed end of the kiln is introduced the 
ore, usually mixed with a slight amount of tar 
or pitch to agglomerate it. As the ore is fed 
and the kiln operated, the contents gradually 
work to a hotter and hotter zone and are finally 
discharged into conveyors, in the form of a 
sintered product varying in size from grains 
to small lumps or nodules. The size of these 
nodules is naturally determined by the details 
of the kiln operation. The process also is most 
beneficial as a desulphurizing agent. The ma- 
terial is now ready for the blast furnace. 

At a number of plants, flue dust taken from 
the dust catcher and piping of the blast furnace 

81 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 

plant is thus treated with excellent results, as 
well as the iron bearing residues of copper ores 
from which the copper has been extracted. 

Briquetting — Briquetting is still another 
method employed for the same purpose as 
nodulizing. The fine ores are mixed with some 
adhesive as a binder, such as tar, rosin, molasses 
and various mineral preparations. The material 
is then pressed into some shape easily handled 
and thoroughly baked. In some instances, the 
ores resulting from wet magnetic separation 
are briquetted without other binder than their 
own moisture, but are subjected to such high 
temperatures in the drying kilns that this 
heat produces a sufficient bond. As is the case 
with nodulizing, briquetting also tends to desul- 
phurize. 

In general, the whole question of ore treat- 
ment, by whatever means, is most vital, and 
on its development depends in a great measure 
the practically unlimited iron production of 
this country. Due to advanced methods both 
of ore treatment and furnace operation, ores 
formerly valueless are today in demand. Vast 
quantities in the Superior region until recently 
considered too highly silicious to be of value, 
now bid fair to be large factors, due to processes 
of concentration recently perfected. 

Although estimates of what may be the 
quantity of the ore bodies comprising the 
available supply must widely differ, due to the 

82 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

varied assumptions made and the many in- 
determinate factors, the ultimate exhaustion 
of the known rich ore bodies within a com- 
paratively definite period seems assured. Never- 
theless, such progress has been and is being 
made in methods of concentration as to insure 
the availability of vast bodies of lean and 
impure ores, and places the date of their ex- 
haustion far in the indefinite future. 



S3 




MATERIALS-FLUXES & FUELS 

CHAPTER III 



LUXES — Composition — As previously 
indicated, the flux is to render fluid 
the gangue of the ore and the ash of 
the fuel, a portion of the furnace 
charge which would otherwise be infusible at 
furnace temperatures, and is also to remove a 
portion of the sulphur in the form of calcium 
sulphide in the slag. 

It is apparent then, that the nature of the 
flux is wholly dependent upon the nature of the 
material to be fluxed; the latter if an acid, 
requiring a basic flux, and vice versa. The 
vast majority of gangues are essentially acidic 
in their composition and consequently, require 
a base to form easily fusible compounds. In 
a few instances, the gangue itself contains such 
proportions of bases and acids as to render it 
practically self-fluxing. 

The cheapest and most available flux is 
limestone, although in some instances lime in 
the form of oyster shells has been employed. 

84 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

It is impossible to obtain a cheap and high 
grade limestone in all localities, consequently, 
recourse is had to one containing more or less 
magnesia or even to a true dolomite containing 
equal parts of calcium and magnesium. A 
charge part of limestone and part of dolomite 
is also often used. 

With small quantities of magnesia, little 
difference is noted, but with larger amounts 
the question has often arisen as to whether it 
holds the sulphur in the slag as well as does the 
limestone. Although opinion is divided, the 
fact remains that in a number of furnaces and in 
widely separated districts the results with the 
use of dolomite are excellent both as to sulphur 
removed and fuel costs. 

Limestone is a carbonate of lime, CaC0 3 , 
together with small quantities of silica and what- 
ever other impurities it may have. The oxide 
CaO being the active agent, CO2 gas is really 
an impurity and this gas must be eliminated 
before the lime is in a position to perform its 
function. 

Theoretically, this elimination can be most 
economically made outside the furnace by 
calcining, and the reason for repeated ex- 
periments along this line is evident when we 
consider just what occurs in the downward 
passage of the stone in the furnace wdien it is 
charged raw. As the stock descends subject 
to increasing temperatures, the stone attains 
a dull red heat at about 1100° F. and here 

85 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

parts with its CO2 gas, according to the 
equation : 

CaC0 3 = CaO + C0 2 
This gas rises with the ascending currents, 
but does not remain as CO2 , for at this heat the 
carbon in the coke has a marked affinity for 
the oxygen in the CO2 and the following re- 
action takes place: 

C0 2 + C = 2 CO. 
This CO passes off through the downcomers. 
In other words, for every pound of carbon in 
the limestone charged, an equal amount is 
abstracted from the furnace fuel and without 
performing any useful work. 

Although calcination of the limestone would 
at first sight seem to overcome this, actual 
practice shows little if any advantage. This is 
due to the fact that CaO has a marked affinity 
for CO2 at temperatures below a red heat, 
and if the flux is introduced into the furnace 
as CaO, it continues to absorb this gas in its 
descent, the CO2 being present in the ascend- 
ing volume of furnace gases. Hence, the 
CaO reverts to limestone, CaCOs, and in turn, 
as it finally gets to a zone where the temperature 
is sufficiently high, the work of decomposition 
is repeated. 

There is also a decided disadvantage in the 
use of the oxide due to its fine condition which 
renders it easily blown from the furnace when 
the blast is at high pressure, w^hile raw lime- 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

stone crushed to pass from 4" to 6" rings is 
of ideal size for the furnace charge. 

Experiments conducted abroad are said to 
show diminished fuel consumption and increased 
tonnage with the use of the oxide, but the 
actual economy when the cost of calcination 
is considered, is little, if any. 

Relative Value of Fluxes — It is ap- 
parent that since the office of the limestone is 
to flux silica, alumina, etc., i.e., the acids in 
the gangue and ash, it also fluxes the acids 
present in its own composition, and its available 
base to apply in fluxing the gangue and ash is 
only whatever may be left after combining 
with the acids which it carries with it. From 
this is seen the importance of a stone low in 
impurities. Assume, for instance, limestone 
with the following analysis: 

Acid Base 

Si0 2 A1 2 3 CaC0 3 MgC0 3 

1.44 2.12 82.55 13.50 

Of CaC0 3 the oxide CaO forms by weight 56% 
Of MgC0 3 the oxide MgO forms by weight 47.6% 

Therefore, 82.55 X .56 = 46.23 Total base in CaC0 3 
13.50 X .476 = 6.43 Total base in MgC0 3 

52.66 Total base. 
1.44 + 2.12 = 3.56 Total acids. 

52.66 — 3.56 = 49.10 
In other words, 49.10% is the available 
base of the flux and is the basis on which a 
comparison between various fluxes must be 

87 



Harbison-Walker Refractories Co., Pittsburgh, Pa 




BY-PRODUCT COKE C 
United Coke & Gas Comp. 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 




INITED OTTO SYSTEM 

ED 
Battery Place, New York 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 




STANDARD BEEHIVE COKE OVEN 



90 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 




fcLr 




__ 







LONGITUDINAL SECTION 

MITCHELL OR BELGIAN COKE OVEN 



91 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 

made, bearing in mind in comparing the 
quantity of CaO and MgO in any two fluxes 
that MgO is 1.4 times as efficient as CaO. 

FUELS 

There are practically but three fuels avail- 
able for blast furnace work, i.e., coke, charcoal 
and anthracite coal. Of these, coke is by far 
the most important, fully 90% of the pig iron 
production in this country being made with 
that fuel, and the proportion is constantly 
increasing. 

The prime essentials of a blast furnace fuel 
are: 

1st. Purity: — It must be high enough 
in fixed carbon to afford necessary 
fuel value, and sufficiently low in 
phosphorus and sulphur that the pig 
iron may not be unduly affected by 
these elements. 
2d. Physical Strength: — It must be 
strong enough to hold up its burden 
without crushing or softening at com- 
paratively high temperatures. 

3d. Porosity: — It must be so open in 
structure as to allow sufficient area of 
combustion for the quick development 
of its heat. 

Coke — Coke is the residue resulting from 
the dry distillation of a coking coal. These 
coals are all bituminous but by no means all 

92 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

the bituminous coals are coking coals, nor will 
anything but actual trial prove conclusively 
whether or not a coal has such properties. 
The analyses of two coals may be practically 
identical, yet one refuse to coke while the other 
is entirely satisfactory. A mixture of a coking 
and non-coking coal may also give good results. 

Coking consists essentially in driving off 
the volatile constituents of the coal, mostly 
hydrocarbons, and a portion of the sulphur, 
the coke residue being the fixed carbon and 
the ash, with whatever sulphur and phos- 
phorus may remain. In coking, the coal 
softens, swells, and becomes a viscous mass 
through which the bubbles of gas find their 
way to the surface and escape, leaving a hard, 
porous, open structure. 

Inasmuch as the volatile matter in some coals 
will run as high as 37% to 38%, (although 18% 
volatile coal has been coked) it is apparent that 
there is a great shrinkage on coking, a ton 
of coal making in the Beehive oven approx- 
imately six-tenths to seven-tenths of a ton of 
coke, with the impurities of one ton of coal 
concentrated in the lesser amount of coke. 
This is not strictly true as regards the sulphur, 
as a portion of this is driven off during the 
process. 

Impurities — The greater portion of the 
sulphur is usually in the form of iron pyrites, 
FeS2, although some may be as a sulphate, in 

93 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 




CROSS SECTION THRU. OVENS 

KOPPERS BY-PRODUCT COKE OVEN 



94 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 




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Harbison- Walker Refractories Co., Pittsburgh, Pa. 




VERTICAL CROSS SECTION 

SEMET-SOLYAY BY-PRODUCT COKE OVEN 



96 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 




SEMET-SOLVAY BY-PRODUCT COKE OVEN 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

which form it remains unchanged in the ash. 
In the Pittsburgh district it is usual to consider 
about 90% of whatever sulphur there may be 
in the coal, to be in the form of iron sulphide 
or pyrites, and of this theoretically, five-sevenths 
may be eliminated in the coking process. From 
this a close estimate of the resultant sulphur 
in the coke may be made. 

Many coals today too high in sulphur and 
too bony, i.e., mingled with slate, can be 
ground and washed, giving a much purer coal 
and also distributing the ash so that the physical 
strength of the coke is improved. 

Phosphorus exists usually in the form of 
phosphate of lime and remains unchanged, 
obviously being of higher percentage in the 
coke than in the coal. 

Coke is made in three types of ovens, i.e., 
the Beehive, the Mitchell or Belgian, and the 
By-product oven. 

Manufacture — Beehive Oven — As its 
name implies, this oven resembles a beehive, 
being nothing more than the section of a vertical 
cylinder about 12 7 6" in diameter, and say 2'8" 
in height, surmounted by a section of vertical 
dome as indicated on page 90. The total height 
of the interior is from 6'6" to 7'6". The oven 
walls are preferably made of high grade fire 
clay brick, made so as to withstand not only 
the heats encountered but the exceptionally 
severe abrasion especially incident to the ma- 
chine-drawn oven. The crown of the oven 

9S 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

should be of a lime bond silica brick, exception- 
ally refractory and one which the experience 
of years has proven to be by far superior to any 
other material. 

At the front of the oven is an opening or 
door to allow the withdrawal of the coke. 

These ovens are built side by side in long 
batteries or banks, as they are sometimes 
called. A suitable loam filling then entirely 
covers the oven and dome, so that the whole 
battery forms one continuous block. Alternate 
ovens are charged and drawn so that each oven 
when freshly charged is fired by the heat of 
adjoining ovens already in blast. 

The door is partially bricked up and the 
oven is charged with coal from a larry through 
an opening in the crown, the amount of such 
charge depending upon whether the coke is 
what is called 48-hour, 72-hour or 96-hour 
coke, i.e., in accordance with the period of 
burning. The longer the time of coking, the 
better the product in every way, the volatile 
matter is more thoroughly eliminated and the 
physical structure strengthened. The majority 
of Beehive blast furnace coke is a 48-hour 
product. 

The charge is then leveled and the door 
bricked to the top with the exception of a small 
space to afford draft, or as it is termed u air" 
the oven. The outside of the door is then 
luted with clay to render it air-tight. The 
heat stored in the oven walls and that trans- 
mitted from adjacent ovens soon raises the 
temperature sufficiently to ignite the gases, 

99 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

which begin to distill. This still further 
raises the temperature and the whole mass 
becomes pasty. There is at first a marked 
swelling with the fusion, but finally, as dis- 
tillation progresses, the mass shrinks to a volume 
considerably less than the original. As the 
process is finally completed, the door is torn 
down and the oven watered, thus causing the 
bed of coke to contract and split so that it 
can be withdrawn. 

The structure of the coke is distinctly 
columnar, being 18 " to 20 " long in the direction 
of the depth of the coke bed. Good Beehive 
coke has a pronounced silvery white luster and 
throughout its mass are shiny nodules formed 
during distillation by the deposition of the 
carbon from hydrocarbons. There are also often 
fine jet-black hairlike filaments from the same 
source, an indication of good coke. The 
essential points to watch are the sulphur and 
phosphorus content and the physical structure 
of the coke. 

The following are fair average analyses of 
dry Beehive coke in the districts indicated. 
These analyses are the average of a week's 
run. 



District 


Vol. 

Per 
Cent 


Fixed 
C. 


Ash 


S. 


P. 


Connellsville. . 


.58 


89.53 


9.89 


.833 


.012 


Latrobe 


.30 


88.05 


11.65 


.949 


.031 


Uniontown . . . 


.38 


89.87 


9.75 


.643 


.013 


Klondyke 


.48 


88.92 


10.60 


.848 


.009 



100 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 

At a number of plants the gases, instead of 
being taken off as previously indicated, at the 
trunnel, are conducted through an opening 
at the back of the oven just above the spring 
line of the crown and are led through waste 
heat flues, to the boilers where they are burned. 
This service is particularly severe on the 
brick for lining but the employment of a high 
grade lime bond silica has in every instance 
given excellent results and seems to have en- 
tirely solved this problem. With this difficulty 
out of the way, there is no question but that 
the practice will largely increase, due to its 
very considerable economy. 

A fair average of the gases from a Beehive 
oven on a Connellsville coal will show: 

C0 2 — 3.0% 

CO — 9.0% 

H 2 —11.0% 

CH 4 — .30% 

N 2 —76.7% 
The analysis varies widely with the airing 
of the oven, but the above may be assumed a 
fair average in good practice. In quantity, 
the amount is theoretically sufficient to supply 
approximately 27 H.P. per oven, and actual 
results have given over 19 H.P. per oven. 

Mitchell, or Belgian Oven — The Mitchell 
oven is a modification of the Belgian type, 
one difference being that it provides an improved 
combustion chamber. The process is essentially 

101 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 

identical with that of the Beehive oven, but 
structural differences in its shape are evident 
as on page 91. In this type there is an open- 
ing at both ends; consequently, the oven 
can be discharged in a few minutes by a pusher 
extending through the oven, thus utilizing 
practically all the heat for the next charge. 
The oven is immediately charged after pushing. 

Although comparatively new in the United 
States, this type bids fair to show very marked 
economies in operation and with greatly de- 
creased loss in braize, or powdered coke, in 
which there is necessarily considerable waste 
in drawing any type of Beehive oven. 

By-product Oven — In this type of oven, 
as the name implies, special attention is given 
to the utilization of the by-products in the 
gases and the gases themselves, after the by- 
products are extracted, are available for fuel. 
There are a number of types working success- 
fully, such as the Koppers, the Otto Hoffmann, 
the Semet-Solvay and others. The illustrations 
on pages 88, 89, 94, 95, 96 and 97 will show 
clearly the outlines. 

In general, the block of ovens form a series 
of narrow coking chambers or retorts from 16" 
to 24 " in width, 5' to 6' high and possibly 30' 
long, with a door at each end. The walls of 
the coking chamber form flues through which a 
portion of the gases of distillation pass and on 
being burned heat the coal as it is freshly 
charged. 

102 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

In the By-product oven, the coal being in 
a comparatively thin body, is more quickly 
coked than in the Beehive oven and can be 
pushed as in the Belgian oven, thus allowing 
little heat to waste. 

Since the coal cokes from the flue walls 
toward the centre of the mass, the gases escape 
here, forming a cleavage plane so that the coke 
is a little less than one-half the length of the 
width of the coking chamber. It is of a dark 
grey color and usually lacks the luster of Bee- 
hive coke. Its analysis usually shows some- 
what higher fixed carbon than Beehive coke 
and it is claimed to be physically as strong, 
if not stronger. There has undoubtedly been 
some prejudice against it in this country, but 
a large number of furnaces are now operating 
very successfully with this form of fuel and 
some of the most important plants are using 
it exclusively. If properly made, By-product 
coke is probably more successful than Beehive 
coke in modern blast furnace practice, due to 
its greater regularity in physical structure and 
chemical analysis. 

The gases are drawn from the top of the 
ovens and treated for the ammonia, tar, etc., 
they contain, all of which is wasted in the Bee- 
hive and Belgian ovens. Where the original 
costs of installation can be borne and where a 
plant is situated favorably as to market, there 
is no question whatever of the enormous 

103 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

economy of the By-product oven over the Bee- 
hive. There is little doubt that its use is 
extending and that it will ultimately displace 
the Beehive oven in this country as it did abroad 
many years ago. Had it not been for the 
seemingly inexhaustible deposits of the highest 
grade coking coals, such as those of the Connells- 
ville fields, and the large returns from the com- 
paratively crude plants erected, operators would 
doubtless have more quickly realized the 
benefits of recovering the by-products of this as 
well as other industrial processes. 

Charcoal — This fuel is the result of the 
dry distillation of wood, i.e., its heating with- 
out access of air. It was formerly made by 
placing the wood in heaps and covering with 
earth, leaving only sufficient openings to secure 
a slight draft. In this way the heat of com- 
bustion of a small portion of the stack serves 
to distill the volatile matter from the remainder, 
and the residue of almost pure carbon remains. 
In certain districts this process is still followed. 

Distillation is now usually performed in 
closed retorts, securing a higher yield of char- 
coal, and the volatile portion is treated for the 
recovery of wood alcohol, tar, etc. 

The charcoal preserves the shape and struc- 
ture of the original wood but loses greatly in 
weight. It is extremely light, of exceptional 
porosity and purity, being low in ash and phos- 

104 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

phorus and with no sulphur. An average 
analysis of charcoal is given as follows: 
Fixed Volatile 

Carbon Matter Moisture Ash P. 

87.25% 6.08% 5.77% 0.92% 0.016% 

It is very friable as compared with coke 
and can support the burden of only a compara- 
tively small furnace stack. 

Charcoal was at one time used throughout 
the country when the adjacent timber land 
could furnish fuel for each local furnace, but with 
the advent of large operations and with the 
added cost as the timber disappeared, its use 
has very rapidly declined until the tonnage 
made on this fuel is a small one. On account 
of its exceptional purity it is still employed 
in the preparation of special charcoal irons in a 
number of furnaces in the southern and northern 
central portions of this country, where timber 
is yet available. 

Anthracite — This coal is used in its 
natural state and has some excellent charac- 
teristics as a blast furnace fuel. If properly 
selected, it is high in fixed carbon, low in ash, 
sulphur and phosphorus and so strong as to 
take any burden. The analysis varies some- 
what widely with various districts from which 
the coal may be taken, but an average of good 
selected anthracite will show about as follows: 

Fixed Volatile 

Carbon Matter Moisture Ash Sulphur 
82.66% 3.95% 3.04% 9.88% .46% 

105 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 

Its great defects, however, are its lack of 
porosity and its tendency to decrepitate or 
break up in small pieces as it is heated in the 
furnace. The first leads to the comparatively 
slow development of its heat, and the second 
to interference with proper passage of the gases 
in the furnace. Almost no stacks are using it 
entirely, although a few mix anthracite coal 
with coke. Even these are slowly being forced 
to the use of coke. It is obvious that on 
account of its high cost, anthracite coal is 
available only w r here there is a comparatively 
short haul, and its consumption is confined 
strictly to its own field of production. 

Valuation of Fuel — Since the office of 
the fuel is primarily to furnish heat, it would 
seem at first sight that such value would be 
directly proportionate to the fixed carbon. This 
would be true, were it not for the fact that the 
ash and sulphur of the fuel must be removed 
by a flux, and the melting of this ash and flux 
requires heat. The available carbon, then, 
is that portion of the fixed carbon remaining 
after deducting whatever carbon is necessary 
to melt the slag formed by the ash and sulphur, 
and the flux required to do this. It is commonly 
estimated that for every pound of ash there 
will be required two pounds of stone, and for 
the sulphur, stone equal to three and one- 

106 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

half times its weight. Assume, for instance, 
a coke analyzing: 

Fixed Carbon 86.50% 

Ash 11.50% 

Sulphur 75% 

11.50 X 2 = 23% stone for ash. 

.75 X 3.5 = 2.62% stone for sulphur 

25.62% stone 
If the stone shows, for instance, 95% 
CaC0 3 , 44% of 95% = 41.8% is C0 2 — a gas; 
consequently, 58.2%, the balance of the stone, 
enters the slag. In other words, in the stone 
to flux ash and sulphur there will be: 
25.62 X .582 = 14.91% 
Hence, total weight slag: 
11.50% ash 

.75% sulphur 
14.91% stone 

27.16% 
or 27.16 pounds per 100 pounds of coke. 

Experience shows that to melt the slag 
requires about 25% of its own weight in carbon. 

25% of 27.16 = 6.79 
Available C = Fixed C (86.50)— 6.79 - 79.71%. 

In this manner, the relative value of any 
fuel is easily determined. 



107 




BURDENING THE FURNACE 



CHAPTER IV 



INTRODUCTORY 

^=n | l/HE burdening of a furnace is the 
determination of the proper propor- 
tions of ore, flux and fuel for the 
furnace charge and is directly de- 
pendent, first, UPON THE ANALYSIS OF THE 

MATERIALS AVAILABLE TO CHARGE INTO THE 

furnace, and second, upon the class of 
iron to be produced, whether basic, bessemer, 
foundry, malleable, low-phosphorus, forge, high 
silicon or whatever its character may be. 
The ability to burden properly was deemed one 
of the "gifts" of the old-time founder or 
operator, regarded with awe by the uninitiated, 
and oftentimes the results accomplished, in 
view of the inexact information at hand, were 
little short of wonderful. The modern laboratory, 
however, with its quick and accurate analyses, 
has done away with much of the old-time guess 
work, but nothing will do away with the neces- 
sity for judgment, experience and a certain 



108 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

intuition which yet seems the possession of 
the most successful furnacemen. Theory and 
the laboratory have their places in the operation 
of the blast furnace and most important ones 
they are, but they are by no means all-sufficient. 
Success can be attained only by trial and 
application of intelligence and experience to 
the ever changing conditions of the furnace. 
The furnace must work freely and regularly 
and must produce the kind of iron desired. 
These results are accomplished by proper 
temperature and by proper composition of 
the slag regulated by the burdening of the 
furnace, and the two are by no means in- 
dependent of each other. 

Slag — Since everything charged into the 
furnace appears either in the iron, slag, or gases, 
it is evident that all the non-volatile constituents 
in the ore, stone and coke which are not to ap- 
pear in the iron must appear in the slag. The 
problem then, is to form such a slag as shall 
have for any impurities which might enter the 
iron, a greater attraction than has the iron, 
and by a proper composition of slags and 
regulation of temperature these results may be 
widely varied. 

Blast furnace slags are essentially silicates 
of lime, the following cited from Campbell 
being typical examples: 



109 



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110 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

These analyses do not include, however, 
a number of extremes which have nevertheless 
given good results in continuous operation. 

From these it will be seen that there is a 
very considerable latitude in the variation of 
the constituents. 

Although the slag is, as mentioned, a silicate 
of lime, either the lime or silica may be and 
usually is, partially replaced by other radicals. 
Few limestones used as fluxes are so pure as to 
be free from magnesia and on the other hand, 
many furnaces use magnesian limestone, and 
some, a true dolomite partially or even entirely 
as a flux. Consequently, the lime of the slag 
is usually partly replaced by magnesia and very 
small quantities of iron, manganese and the 
alkalies. The silica is also always accompanied 
by alumina in greater or less proportions and 
by more or less sulphur acting in the form 
of calcium sulphide, CaS, as an acid radical. 
Inasmuch as none of the elements can enter 
the iron except in the reduced condition, we 
can determine at the outset which will be present 
by the test as to whether or not they are reduced 
or deoxidized under blast furnace conditions. 
As the lime, alumina, magnesia and whatever 
alkaline bases may be present are not reducible, 
whatever amount is in the ore, stone and coke 
will be in the slag; the same is true of the major 
portion of the silica, although some of it is re- 
duced to silicon and enters the iron. Just how 

111 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 

much is dependent on the operation of the fur- 
nace and the character of the slag. Sulphur 
also combines with the iron to a greater or 
less degree, in accordance with the temperature 
of the furnace and the character of the slag. 
The same is true of manganese. Practically all 
the phosphorus in the charge will be found in 
the iron. There are then, only the silicon, sul- 
phur and manganese, over which there is any 
regularity in- the control. 

Composition — In considering the con- 
stituents indicated in the previous analyses of 
slags, there is little difficulty in placing them 
definitely as acids or bases, with the exception 
of alumina. It occurs in slags apparently 
sometimes on one side of the dividing line, 
sometimes on the other, but in its effect, is so 
nearly neutral that any error, if error there 
be in assuming it to act as an acid with the 
silica as is usually done, is of comparatively 
small moment. 

The sum of the silica and alumina is usually 
taken as the measure of the slag's acidity and 
with this assumption a reference to the analysis 
shows most slags as basic compounds, although 
this is by no means always the case. 

As a general rule, the sum of the silica and 
alumina will range somewhat under 50% of 
the slag, alumina running usually about one- 
third of this amount, the exact ratio of the one 
to the other being dependent on the original 

112 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

amounts in the flux used; but the proportion 
of the slag as a whole which they make up is 
dependent on the amount of stone used in the 
charge. With the sum of the silica and alumina 
constant, there may be a very considerable 
variation in the relative proportions of the two 
without marked changes in the characteristics 
of the slag, although as a whole a basic slag 
exhibits more marked basicity with high 
alumina and low silica than with low alumina 
and high silica. The converse is also true. 

The sum of the basic constituents, lime and 
magnesia, usually forms about one-half the 
slag. Here again the ratio of one to the other 
is dependent on their ratio in the flux except 
as somewhat affected by the lime and magnesia 
content in the gangue of the ore and ash of 
the coke. 

As in the case of alumina combined with 
silica, so there may be here considerable 
variation in the ratio of magnesia to that of 
lime without marked change in its char- 
acteristics, provided the sum of the two remains 
about the same. However, with high alumina 
and high magnesia both occurring, the slag 
usually tends to become too viscous on account 
of its extreme refractoriness. 

Control — The slag and the temperature 
of the furnace have previously been referred to 
as the agents for the control of silicon, sulphur 
and manganese, and the inter-relation of the 

113 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 

two may again be emphasized. In general, 
the more basic a slag, the more refractory it is, 
although it is also true that a highly acid slag 
is generally refractory. There is, then, a means 
for decreasing the fusibility of the slag by 
increasing its basicity, i.e., increasing the pro- 
portion of flux. At first sight it may seem 
that if the hearth is too cold, the temperature 
might be raised without regard to the com- 
position of the slag, but this is true only within 
comparatively narrow limits, for the iron, ac- 
quiring most of its heat in passing through the 
hot slag, is in a great measure dependent upon 
it for any increase in temperature. An easily 
fusible slag is naturally but a short time within 
zone of fusion, quickly melting and forming 
a layer of slag over such iron as may be in the 
hearth and effectually prevents the transmission 
of any large quantities of heat through it, how- 
ever hot the furnace may be at or above the 
tuyeres. With a more infusible slag, on the 
other hand, and one consequently longer in 
the heat zone, it absorbs more heat in its passage 
to the hearth and the iron trickling through it 
in a molten condition, the temperature of the 
iron is correspondingly raised. The relation 
of temperature and slag composition is an 
inseparable one. 

Both the above, i.e., increased basicity and 
high temperature, have a marked influence on 
the control of the silicon and sulphur, a high 

114 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

temperature in general favoring the reduction 
or deoxidation of silicon and its incorporation 
in the iron. However, the basic slag has a 
strong affinity for the silica and tends to 
neutralize the effect of temperature, keeping 
the silica unreduced in the slag. The basicity 
of the slag also has the effect of holding a large 
portion of the sulphur in it, as in the case of an 
open hearth slag, and results in low sulphur in 
the pig iron. Hence the final result will be, 
in general, low silicon and low sulphur in the 
pig with a high temperature and decidedly 
basic slag, and a constant increase in both 
silicon and sulphur as the slag changes in its 
scale from basic toward acid properties. 

The combining limit of sulphur in basic 
slags is usually considered to be not over 2%, 
although some instances can be cited in which 
the slag averaged during considerable periods 
2.4%, often running as high as 2.8% in sulphur. 
Because of the limit of solubility, it is essential 
that the slag be sufficient in volume. This is 
the case in the gangue of a large majority of 
ores, but where the slag is scant, a silicious 
ore, mill cinder, or even sand may be used, 
and its acidity neutralized by additional lime- 
stone. 

The control of manganese is affected by the 
temperature and composition of slag, as is 
silicon and sulphur. A high temperature favors 
its reduction and, being a definite base, a highly 

115 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

basic slag has less hold upon it than has an 
acid slag and allows more of the metal to be 
reduced and enter the iron, while with acid 
slag it is obvious there is less tendency for the 
manganese to appear in the pig. It is of marked 
benefit in the removal of sulphur, forming a 
sulphide MnS, thus decreasing the sulphur in 
the iron. This property is utilized, as has 
previously been shown, in the removal of sul- 
phur in open hearth slags. 

Detail of Problem in Burdening — In 
order to w r ork out the theoretical burden of 
the furnace, it is of course necessary to have 
accurate average analyses of the component 
parts and an idea of the analysis of the iron it 
is desired to make. 

For the sake of illustration it is assumed 
that the pig iron desired will be, say 94.5% Fe, 
silicon 1.5% and total carbon 3.5%, the average 
analyses of the materials from which it is to 
be made being as follows: 

Material SiO, 

Fuel — Connellsville Coke . . . 5.40 

Ore — Ashland, Gogebic. . . . 6.34 

Flux — Limestone 1.44 

(Continued) 

Material Mn P 

Fuel — Connellsville Coke. . . .012 
Ore —Ashland, Gogebic .30 .04 

Flux — Limestone 005 

It is assumed furthermore, that the ratio 
of the acids to the bases in the slag will be as 

116 



M 2 0» 


CaO 


MgO 


2.90 


.90 


.69 


2.70 


.38 


.24 


2.12 


46.23 


6.43 


S 


Fe 


C 


.83 




89.5 


.009 


53.49 





Harbisox-Walker Refractories Co., Pittsburgh, Pa. 

1 is to 1.2, a common ratio in smooth running 
slags. 

The first step is to find the amount of flux 
needed for the fuel and for the ore. To do this 
it is necessary to find its available base as 
indicated on page 87, as only such proportion 
of its bases are free to act as flux for the fuel- 
ash and ore as are left after fluxing the acids 
in its own composition. 

Flux — Available base and weight of slag. 
Acids Bases 

Si0 2 1.42 CaO 46.23 

A1 2 3 ^12_ MgO 6 .43 

3.54 52.66 

3.54 X 1.2 (bases in slag = 1.2 X acids) -4.25 

bases needed. 

52.66 (bases present) — 4.25 (bases needed) = 

48.41, surplus or available base. 

Weight of slag formed = 

Si0 2 + AI2O3 + CaO + MgO 

1.42 + 2.12 + 46.23 + 6.43 = 56.20% 

[weight of stone. 

Fuel — Flux needed, weight of slag and 
available carbon (page 107). 

Acids Bases 

Si0 2 5.40 CaO .90 

AI2O3 ^90 MgO _^69 

8.30 1.59 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

8.30 X 1.2 (ratio to bases acids) = 9.96 bases 

[needed. 

9.96 (bases needed) — 1.59 (bases present) = 
8.37 deficiency to be made up by the lime- 
stone. 

In each pound of limestone there is .484 lbs., 

8 37 
available base, so that — — = 17.29 lbs. lime- 
stone to flux ash. 

To flux the sulphur it will require an amount 
proportional to their atomic weights : — 

CaO : S : : X : .83 

(56) (3 ) 

X = 1.45 lbs. of the oxide, or, 

1.45 

— — = 3.02 lbs. limestone. 
.48 
17.29 + 3.02 = 20.31 lbs. stone per 100 lbs. 
fuel. 

Weight of slag formed = 

8.30 + 1.59 + .83 + (20.31 X .562) = 22.13 

[lbs. 

The usual assumption that the slag requires 
25% of its weight in carbon to melt it, is 
sufficiently close for practical purposes. 
25% of 22.13 = 5.53 lbs. carbon. 
89.5 (fixed C) — 5.53 = 83.97 available carbon. 

Ore — Flux needed, weight of slag. 
Acids Bases 

Si0 2 6.34 CaO .38 

A1 2 3 2.70 MgO .24 

q Q4 MnO .13 (Assume J^ goes in- 
- — to slag as oxide.) 

.75 

118 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

Since the pig is to be 94.5% metallic iron 
and the ore is 53.49% iron, it is obvious that 

94.5 
it will require or 1.767 tons of ore for one 

ton of pig iron. 

The pig is to have 1.5% Si which is reduced 
from the silica in the gangue of the ore, or in 
other words, 1.5 lbs. silicon for each 100 lbs. 
of pig. 

— X 1.5 = 3.21 lbs. silica, Si0 2 

28 

There is, then, 3.21 lbs. of Si02 in the 176.7 lbs., 
of ore which it is unnecessary to flux, equal to 
1.87% Si0 2 . 

9.04—1.87 = 7.17 

7.17 X 1.2 (ratio bases to acids in slag) = 

8.60 bases needed. 
8.60 (bases needed) — .75 (bases present) = 
7.85 deficiency to be made up by 

limestone. 

7 g^ 

= 16.22 lbs. stone per 100 lbs. ore. 

.484 H 

1.767 X .1622 = .2866 tons stone per ton pig. 

Weight of slag formed from ore = 

(.0717 + .0075) X 1.767 = .1399 tons. 

Weight of slag formed from stone = 

.562 X .2866 = .1611 tons. 

.1399 + .1611 = .301 total slag from ore per 

[ton of pig. 

Fuel Requirements — As noted before, 
practice has shown approximately 25% carbon 

119 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 

required for melting the slag so that .301 X .25 
= .075 parts carbon for this item. To this must 
be added carbon for reducing and melting the 
pig and for its impregnation with carbon. 

In the average furnace the careful calculation 
of the heat balance, that is the determination 
of all sources of heat which enter the hearth, 
and the accounting of the heat given off or 
absorbed in one form or another shows that 
about 66 lbs. of carbon is required for the 
reduction, impregnation with carbon and melt- 
ing of each 100 lbs. of 1% silicon pig iron, 
with an extra 5 lbs. of carbon for each 1% of 
silicon. The amount is accurately determined 
only by the heat balance, and is dependent on 
the temperature and volume of the blast, the 
character of the burden, temperature and 
volume of the gases, the carbon ratio, 
temperature, weight of slag and iron, etc., but 
with a blast at about 1000° F. the above figure 
is sufficiently close for the purpose. For the 
reduction, impregnation and melting of 1.5% 
silicon pig there is needed: 

.66 + .025 = .685 parts carbon. 
.685 (carbon for pig) + .075 (carbon for 
slag) = .76 parts carbon. 

With coke of 83.97 available carbon there is 
required : 

.76 

——X 2240 = 2027 lbs. coke per ton of pig, 

.oo97 

or, adding 3% for braize, 2100 lbs. 

120 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

The slag from the ore per ton of pig will equal 
.301 X 2240 = 674 lbs. and from the coke, 
.2231 X 2027 = 452 lbs., or a total of 1126 lbs. 
per ton of pig. 
The total stone will be, for the ore, 

.2866 X 2240 = 542 lbs., and for the coke, 

.2213 X 2027 = 448 lbs., or a total of 990 lbs. 

The basis of the charge is taken as the fuel, 
and the ore and stone proportioned accordingly 
as above. The amount of fuel in the " round" 
as it is termed, varies with the size of the furnace, 
— in a fairly good sized furnace being 5 gross 
tons. On this basis, the charge in the above 
proportions would be : 

Coke 11,200 lbs. 

Ore 22,000 lbs. 

Stone 5,500 lbs. 

The coke charge is usually kept constant and 
the ore and stone varied to suit the condition 
of the furnace operation as it changes from 
time to time. 



121 




OPERATING t6<? FURNACE 



CHAPTER V 



BLOWING IN 




*HEN a new furnace is to be blown 
in or an old one has been relined, 
the first operation is to thoroughly 
dry out the brickwork. Although the 
brick, if properly laid, are with the thinnest 
possible joints, yet each course is bedded in 
a grouting or slurry of fire clay and all inter- 
stices filled with it so that there is in reality 
a large amount of water to be evaporated 
before the furnace lining is thoroughly dry. 
This drying is accomplished either by wood 
fires built in the hearth or by gas burners inserted 
there. The fire should be but light at first, 
increasing in intensity as the furnace dries. 
Often ten days to two weeks is considered 
sufficient time in which to do this work, but 
two weeks should be the minimum limit. In 
view of the immense importance of the lining 
as affecting the life of the furnace, too much 



122 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

stress cannot be laid upon the necessity for its 
thorough drying-out. 

In a number of instances the development 
of hot spots soon after blowing in has un- 
doubtedly been due to shrinkage cracks open- 
ing up in the mass of brickwork because of 
premature blowing in of a too green furnace. 
However, the realization that the saving of a 
few days at one end of the campaign may be 
made at cost of months on the other, has 
undoubtedly led to a more rational view of the 
situation. 

It is common practice to spread on the 
bottom of the furnace hearth two or three feet of 
coke braize. This serves to prevent chilling of 
the first iron melted, as well as chilling of the iron 
notch which sometimes occurs when this pre- 
caution is omitted. Upon the braize is charged 
coke, well up toward the tuyeres, then a mass of 
kindling wood covered in turn with charcoal 
for a couple of feet in thickness, surmounted 
by a blank of coke extending at least above the 
mantle. This procedure is sometimes varied 
by the use of layers of cord wood on end, 
placed either at the bottom of the hearth and 
extending up 12 to 16 feet, or the wood may 
be started on a scaffold at or about the level 
of the tuyeres, the space beneath being filled 
with kindling. With the coke blank is charged 
a small quantity of limestone sufficient to flux 
the ash of the coke, as well as sometimes a 

123 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

certain amount of slag to increase the volume 
of slag and "wash" out the hearth. 

The charges of fuel, ore and flux are now 
begun, but with a much larger fuel ratio than 
when the furnace is in operation, the ratio de- 
creasing gradually toward the top so that it is 
about one to one when the furnace is filled and 
ready to light. The burden or proportion of 
ore is gradually increased as the furnace is 
operated until in about two weeks it is carrying 
its normal burden. 

The furnace is lighted through the tuyeres 
with all openings save the bleeder tightly closed, 
the valves at stoves and boilers also shut; a 
light blast is then turned on. The smoky 
gas which soon appears at the bleeder is ignited 
and allowed to burn until the smoke dis- 
appears, showing that the wood is consumed. 
The bleeder is then closed and the valve farthest 
from the furnace on the boiler line may be 
opened and lighted after the gas has had 
sufficient interval to pass through the down- 
comer and piping, forcing out the contained air. 
Every care is necessary, as explosions are very 
liable to occur should the gas mingled with 
air come in contact with a flame. At certain 
plants it is an invariable rule that the gas 
shall not be lighted until 48 hours after start- 
ing. 

Soon after the furnace is lighted, the slag 
begins to accumulate in the hearth and a little 

124 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 

later, the iron as well. As soon as the slag 
reaches about the level of the tuyeres it is drawn 
off at the cinder notch and this operation re- 
peated as often as necessary until sufficient 
iron has accumulated to tap. The first iron 
is liable to be "off" iron, i.e., it is not of the 
proper grade or analysis, as it is at this time 
impossible to have such temperature and com- 
position of slag as to produce iron of given 
analysis. Within a few casts, however, the 
furnace is usually brought up to the production 
of iron of the grade desired. 

Charging — In the modern automatic skip- 
filled furnace, the stock is usually dumped from 
the railroad cars into bins from which it is 
run direct to larry cars, automatically weighed, 
and from these dumps into the skips. 

As the furnace continues in operation, the 
column of material constantly descends and the 
furnace is as constantly filled at the top by what- 
ever may be the filling and distributing device 
used. 

The furnace is charged by "rounds," i.e., 
so many pounds of fuel, ore and coke constitute 
a round. The fuel usually is a constant any- 
where from 5,000 to 15,000 pounds in weight, 
dependent on the size of the furnace, while the 
ore and stone are varied to suit the varying 
requirements of output as influenced by the 
operation of the furnace. The fuel is usually 
charged first, then the ore and stone, this order 

125 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

being maintained with each round. As it is 
most important that the height of the stock 
be kept fairly constant and well up to the 
top of the furnace, it is continually tested by 
rods inserted at the top or is followed by some 
form of automatic stock recorder. 

Operation of Furnace — In general, the 
condition of the furnace and its operation are 
best told by the character of the slag and iron 
it is producing. The relative temperature of 
the hearth can also be w^ell judged by its appear- 
ance as seen through the eye-sights at the 
tuyeres. The color of the hearth interior will 
vary from a dull red tint when the furnace is 
"cold," a temperature at w T hich the outlines of 
the coke, etc., are easily seen, to an incandescent 
white heat. The appearance of the hearth 
as noted merely serves as a check in the 
determination of its temperature, but is most 
clearly evidenced by the character of its product. 
The slag gives a very good indication, the 
desideratum being that it be hot, fluid and grey. 

As previously indicated, it is impossible to 
get hot iron without having a hot slag, but the 
slag although hot may be so difficult to fuse 
as to be viscous and fail to flow clean from the 
furnace. Furthermore, unless fluid, it fails 
in a measure to fully perform its function as 
the various impurities are by no means as 
readily soluble in it. Its fluidity, in fact, acts 
much like that of water, serving as a vehicle 

126 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

of solution for any given compounds which 
it may hold dissolved. 

A slag, on the other hand, may be so fusible 
as to be very fluid at comparatively low 
temperature and so pass through the furnace 
quickly, without attaining a temperature which 
enables it to completely perform its office. Such 
a scouring slag is often very destructive in its 
action upon the furnace lining. 

Its color gives a good indication of its 
composition as well as of the temperature of 
its formation. Hot basic slags usually show a 
greyish color and granular fracture when cold. 
A few very high in lime tend to crumble and 
slake on continued exposure to the atmosphere. 
As the composition of the slag becomes more 
and more highly acid, a vitreous appearance is 
noticeable on the outer edges of the fractured 
piece, this vitreous condition extending deeper 
and deeper in accordance with the acidity of 
its composition. Slags from a cold furnace are 
usually darker in color and also vitreous. Their 
glassy appearance is due, in a measure, to the 
excess of silica, less having been reduced and 
incorporated in the iron as silicon. This excess 
of silica in the slag tends to absorb more oxide 
of iron, giving a darker color. 

Should the furnace be running too hot and 
with a given burden reducing too much silicon, 
i.e., producing an iron too high in silicon, its 
temperature may be reduced by a proper 

127 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

change in the burden, increasing the proportion 
of ore. The effect of such a change would be 
felt only after the new burden had reached 
the hearth but in spite of this delay such 
practice wx>uld be much preferable to the 
introduction of cold blast which would tend 
to raise the fusion zone higher in the furnace. 
It is the aim of the furnace manager to operate 
under as nearly constant conditions as possible 
and the quantity of w^ind blown into the furnace 
is kept practically constant as well as the 
temperature of the blast. 

Should the hearth temperature become 
lower, the amount of silicon reduced becomes 
less and less and the sulphur increases. This 
condition affects also the carbon in the iron, 
not appreciably as regards its total quantity 
but as determining what proportion of the 
carbon shall be in the form of combined carbon 
and what graphitic. In this instance, with 
low silicon and high sulphur, the major portion 
of the carbon is permitted to remain in the 
combined form, producing mottled or white 
iron, an off grade. 

The rise in sulphur accompanying the drop 
in silicon due to a cold hearth is attributable 
in a measure to the following causes: 

1st. Decreased basicity of slag due to its 

greater silicon content. 
2d. Excluding action of silicon upon sul- 
phur in the molten metal. 

128 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

In addition to the above effects of the cold 
hearth, there sometimes occurs floating on the 
slag or entangled with it, what is known as 
"buck shot." This is iron which is but partly 
carburized and at the temperature of the furnace 
has been unable to penetrate the slag and mingle 
with the remainder in the hearth. These shot 
will analyze considerably higher in sulphur than 
the run of the iron. 

The remedy for the above condition de- 
pends on its severity. If the tendency is but 
slight, the putting on of a fresh stove may 
be sufficient. Continued coldness, however, 
indicates that the burden is too heavy and 
the quantity of ore must be diminished. The 
total carbon is little influenced either by the 
burden of the furnace or the temperature as 
such. It is, however, influenced indirectly by 
whatever affects the silicon content of the iron, 
because of the excluding effect of this element. 
Phosphorus also has the same tendency. Irons 
high in manganese on the other hand have an 
attraction for carbon and this element is con- 
sequently higher in iron with a considerable 
percentage of manganese. In general, the total 
carbon in the ordinary class of pig irons runs 
very closely from 3% to 4%. 

Banking the Furnace — For one reason or 
another it is sometimes necessary to curtail the 
production of a furnace, leaving it in condition 
to start on short notice. This is usually done 

129 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

by charging a heavy fuel blank of coke together 
with enough stone to flux its ash, the amount 
of such coke dependent on the time which the 
furnace will probably be idle. This is followed 
by light charges of ore much below the normal 
amount and these, in turn, often by a blanket 
of fine ore serving to seal the interstices. As 
soon as the coke blank reaches the bottom 
of the furnace, the blast is taken off, the furnace 
tapped clear of iron and slag, the tuyeres re- 
moved and all openings bricked up and luted 
with clay as nearly air-tight as possible. With 
this procedure there is comparatively little 
opportunity for combustion to occur in the 
furnace. When the furnace is again to be 
put in operation it will usually be found that 
the stock has been somewhat reduced by the 
very slow combustion that has occurred with 
the small quantities of air unavoidably ad- 
mitted. Just how much the stock is lowered 
depends, of course, on how well the work has 
been done and how long the furnace has been 
banked, but it is perfectly possible to close the 
furnace so tightly that after the first few days 
no settling whatever occurs. If any settling 
has occurred the furnace is then filled with 
very light charges of coke and ore, or with merely 
a blank of coke. The ashes are raked out 
through the tuyere openings, the tuyeres in- 
serted and the blast put on. In this way the 
furnace will, within a few casts, be making 
good iron. 

130 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

There are circumstances where there is no 
time for the preparation of banking the furnace 
as outlined above. In such a case nothing 
can be done except to tap the iron and cinder, 
remove the tuyeres and close all openings 
tightly. It is naturally a much more lengthy 
and difficult matter to start again under such 
circumstances, and it is necessary to cut through 
the chilled material at the iron and cinder 
notches before the furnace can again be put in 
operation. Dynamite may even be a necessity 
to break up the frozen material in the hearth. 
On putting on the blast, very light charges of 
ore are used with blanks of coke so that the 
hearth may successfully regain its lost heat. 

Blowing Out — In blowing out the furnace 
for relining or such repairs as necessitate the 
ending of its campaign, charging is stopped 
and the stock allowed to settle. The top 
becomes very hot under such circumstances, 
and it is usually necessary to cool the interior 
of the furnace by water sprays to avoid ex- 
plosions. As soon as the stock gets within a few 
feet of the tuyeres, the blast is taken off, tuyeres 
removed and the balance of the stock shoveled 
out, when the furnace is ready for dismantling. 

Operation of Stoves — Assume a typical 
plant of four stoves. After erection, the brick- 
work of the stoves should be dried out with a 
slow fire in much the same manner as the furnace 
proper and when it is desired to blow in, a 

131 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 

heavy wood fire is built in each at the base of 
the combustion chamber. This is usually 
succeeded by a coal fire, bringing the stoves to 
as high a temperature as possible by this means. 

The "raw" gas from the furnace as the latter 
is lighted, is then turned on all four stoves as 
the gas is forced from the furnace by the light 
blast from the blowing engines which, at this 
period, are operating at but a fraction of their 
normal speed. Due to furnace conditions, this 
gas is naturally much higher in CO than when 
the furnace is operating regularly. When mixed 
with air the gas is highly explosive. 

After the raw gas has been allowed to burn 
in the stoves for some time and has thus raised 
the temperature to say 800° or 900° F. the blast 
from the engine is forced through one of these 
stoves while the other three are still on gas. 

This single stove in from one-half hour to an 
hour is then cut out and a fresh stove put on, 
the furnace thus gradually working up to normal 
conditions, when with a four-stove plant any 
given one will be in blast one hour and on gas 
three hours. 

The more usual method is to keep the stove 
on for a definite time, normally an hour, re- 
gardless of the precise drop in temperature 
within that period, rather than to put on a 
fresh stove after a drop through any exact 
temperature range. This procedure may be 

132 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

varied somewhat as made necessary by chang- 
ing conditions in the furnace. 

Cleaning — More or less frequent cleaning 
of the stove is necessitated by the accumulations 
of flue dust formed of minute particles of coke, 
ore and limestone carried over by the blast. 
Fragments of brickwork are also dislodged and 
collect in the flues, thus choking them and 
interfering with the blast. The amount of 
flue dust which may accumulate varies widely 
with the operation of the furnace and the 
character of the burden; with fine, soft ores 
there is naturally more dust carried over than 
with coarser ores of the same approximate 
composition, and conditions are often aggravated 
by hard driving. Moreover, with certain ores 
such as those which burden the furnace for 
ferro-manganese, much trouble is experienced 
from the accumulation of dust, although the 
ores in their natural condition are neither soft 
nor fine. In the furnace they readily dis- 
integrate to a powdered form and are carried 
over by the blast, making the gas dirty. The 
effect of any considerable accumulation of 
dust in the stoves as it clings to the flue walls, 
is to greatly reduce the heating capacity, 
as accumulations offer much resistance to the 
taking on and giving off of heat. This may be- 
come in a short time so aggravated that the 
stove is practically without efficiency unless 
cleaned. 

133 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 

Another serious trouble occasioned by flue 
dust of certain compositions is the severe 
fluxing action on the brickwork at stove tem- 
peratures. This is due to the lime and other 
fluxes in the dust and is in some instances 
sufficient to lower the refractoriness of the brick 
several hundred degrees, completely honey- 
combing the top checkers where accumulation 
is greatest. 

In a plant of any size the cleaning crew is 
always at work unless the gas is first passed 
through some form of washer or scrubber, 
and the stove will often require some attention 
at least every two or three weeks. Cleaning is 
accomplished by weighted brushes and scrapers 
let down through the flues and the accumulation 
is then shoveled through the cleaning doors 
at the bottom. 

Furnace Troubles — There are few 
situations where experience is of more value 
and where prompt and decisive action is more 
necessary than with the management of a 
blast furnace plant when trouble occurs. 

Destruction of Lining — The trouble with 
a lining usually shows itself in a hot spot or the 
heating of the shell at various heights above the 
mantle. This may occur at any time from a 
few weeks to months, or even much longer after 
blowing in, and results either from a crack in 
the lining which allows the hot furnace gases 
to reach the shell or from the wearing away of 

134 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

the lining in a particular spot so thin that the 
heat affects the shell. The usual treatment is 
to put on a water spray, thus keeping the plates 
cool, and if the spot is fairly high in the furnace 
the lining will sometimes build up so that the 
spray may ultimately be discontinued or the 
spot at least does not increase in area. If due 
to a crack in the lining, grouting is often pumped 
in through a hole in the shell, and with this aid 
the lining may then give entirely satisfactory 
life. 

As to the causes of the trouble, there are a 
number of contributory conditions which may 
have considerable to do with it, but as the action 
goes on entirely hidden from view, it is naturally 
often difficult to point definitely to the exact 
cause in any given case. 

There is no question whatever that faulty 
stock distribution has been more than any other 
one thing the main factor in these troubles. A 
case in point is that of four new furnaces suc- 
cessively going into blast at one plant at intervals 
of but a few weeks, all on the same burden and 
with the same brands of material for lining. 
After a few weeks run, each developed a hot 
spot at exactly the same location, about 20' 
above the bosh and on the side opposite the 
skip. It was, of course, beyond the bounds 
of possibility that, had any material in the 
lining been defective, it should have by chance 
been collected in each instance in the same spot 

135 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 

and trouble occur nowhere else. A change in 
the method of stock distribution completely 
remedied the difficulty. The skips so dumped 
as to allow the coarser and heavier portions of 
the material to roll to one side and the furnace 
gases taking the line of least resistance, 
channeled up that side. The use of soft coke 
also accentuates any defects in the stock 
distributing device and in a number of instances 
has undoubtedly been the prime factor in 
causing furnace troubles. A bell that is not 
properly proportioned will also cause the same 
difficulty. The large number of tops and dis- 
tributing devices which have been designed to 
overcome this difficulty indicate the importance 
attached to it by blast furnace men. 

Subject as the lining is, not only to the severe 
abrasion of the stock as it is charged into the 
furnace and continues on its way downward, 
but to the fluxing and disintegrating effect 
of the molten and semi-molten mass at all 
points below the fusion zone, it is yet somewhat 
protected from the above, and from the action 
of the corroding gases by the carbon coating 
deposited on the brickwork soon after the 
furnace is blown in. 

The majority of managers realize the im- 
portance of this phase of operation and allow 
sufficient time for such carbon deposit to form. 
It is undoubtedly assisted in its formation by 
the running of a hot and basic slag. 

136 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

Another evil of too hastily bringing the 
furnace up to normal working conditions is the 
opening up of shrinkage cracks which may 
extend entirely through the wall to the furnace 
shell. The cause for this has already been 
discussed but the fact will bear emphasis. 
Xot only should the brickwork of the furnace 
be well dried out before the furnace is lighted 
but even then a considerable period should 
elapse before it is brought up to maximum 
capacity. In certain plants, having record 
output and minimum costs, four weeks' time 
is not considered too long. 

In a number of cases the lining has ap- 
parently melted and worn away at a point so 
high as to preclude the possibility of sufficient 
heat to affect fire brick of even a very mediocre 
grade under normal conditions, this pointing 
to the evidence of fluxing action. 

The height at which this trouble occurs 
corresponds with the height at which are de- 
posited the alkaline carbonates referred to in 
the succeeding chapter and experiments as to 
the effect of such carbonates on high grade 
refractory material in test kilns show that so 
active are these fluxes in combination with the 
clay as to greatly lower the point of fusion. 
Although not positively determined, there seems 
little question that this fluxing action occurs as 
above outlined. 

137 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

Break-Outs - — The lining may be destroyed 
and a break-out occur at almost any point below 
the melting zone, but is usually more serious 
when below the line of the slag or iron. A 
break-out in the bottom of the hearth may 
allow the iron to escape and find its way out 
under the foundations. Inasmuch as molten 
iron as such has little or no action in 
disintegrating brickwork, the opening of cracks 
or fissures in the hearth is due to rupture from 
expansion, settling foundation or defective 
work in laying the bottoms. 

Loss of Tuyeres and Cooler Plates — 
The most frequent and annoying cause of trouble 
is the burning or melting of the tuyeres, which 
occurs from one of two causes, i.e., stoppage of 
water supply or the action of molten iron on the 
metal of the tuyere. In the case of stoppage 
of water supply, the water in the nose of the 
tuyere is soon turned to steam and the metal 
then burns away. 

Normally the tuyeres are considerably above 
the line of the molten iron, but in case of 
an explosion or slip, portions of the charge 
are sometimes projected into the hearth, raising 
the iron and slag temporarily above the tuyere 
level. They are also subject to the dripping 
of the molten iron as it emerges from the 
fusion zone and drops through the slag to 
the hearth. The tuyere nose is often partially 
protected by accumulations from the stock, 

138 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

but the mass of semi-molten material may 
at any time so arrange itself as to allow the 
dripping iron to impinge directly upon the 
tuyeres, in which case, if long continued, the 
iron forms an alloy with the bronze or copper 
and melts away. 

A leaky tuyere is more often evident by its 
effect upon the product of the furnace than in 
any other way. The effect of the water dis- 
charged in the hearth is, of course, to cool it, 
and there is then encountered the dark, vitreous 
cinder common to cold hearths and a cor- 
responding rise in the sulphur of the iron. It 
is also sometimes shown by the increase in 
hydrogen in the escaping gases and may first 
be brought to the attention of the furnace 
man by the back-firing of the gases in gas 
engines of certain types where such are installed. 

The only thing to do is to replace the tuyere 
as soon as possible, which is done by shutting 
off the blast, disconnecting and jarring loose 
the defective tuyere and inserting a new one. 

Pillaring — This condition of the stock in 
the hearth is essentially due to insufficient 
penetration of the blast, and occurs as a column 
of comparatively cold stock usually at the 
center of the hearth. The remedy is either 
decreasing of the tuyere area or increasing the 
blast to secure better penetration. It may be 
sometimes necessary to put in additional tuyeres. 

139 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

Scaffolding — Scaffolding usually occurs 
either in the upper portion of the bosh wall or 
the extreme bottom portion of the inwall; 
in other words, at about the region of the mantle, 
and it is due to the adherence or building out 
of the stock partially supported by the walls of 
the furnace. It is primarily due to contraction 
in the zone of fusion which in turn may be 
attributed to any of the different causes pro- 
ducing irregular working. If the zone of fusion 
is, for instance, suddenly lowered, the pasty 
mass at its top tends to adhere to the surround- 
ing wall, forming an incrustation projecting 
into the furnace. This mass offers severe 
obstruction to the passage of the gases and to 
the descending stock. The gases are driven 
to one side and may even cut out and channel 
the furnace wall on the side opposite the 
scaffold. Anything which will temporarily raise 
the zone of fusion may soften the obstruction, 
when, if the engines are slackened, the obstruc- 
tion may often be loosened by the weight of 
the burden above. 

The trouble may become so severe as to 
require more stringent methods, such as the 
insertion of an extra tuyere or even the use of 
dynamite. Continued trouble from this source 
is usually due to faulty design of the furnace, 
too heavy burden, too much flux or any of the 
numerous factors which tend to irregular work- 
ing. 

140 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

When the incrustation falls away, it often 
brings with it a mass of brickwork, leaving a 
hole where the stock tends to lodge and in- 
creasing the chances of further hanging, par- 
ticularly as the freshly fractured brick is pro- 
tected by no carbon coating. 

Wedging — This term is often used to 
describe the condition of the stock in the upper 
portion of the furnace when it becomes so tightly 
wedged or bound for the time being as to prevent 
its falling. It is due to carbon deposition and 
naturally occurs with those ores which deposit 
the larger amount of carbon in their reduction. 
It is more particularly prevalent with the 
Mesabi ores and does not occur with the Mag- 
netites, however fine may be their state of 
sub-division. In some cases the deposit is 
much more than the original volume of ore, 
so that the tendency to wedging and cor- 
responding obstruction to the descent of the 
stock is easily explained. As the effect of the 
deposited carbon is to fill the voids in the stock, 
the mass becomes exceedingly dense and the 
gas can with difficulty penetrate it. The 
pressure of the blast usually rises rapidly, the 
stock beneath meanwhile settling until at length 
the wedged stock falls. This is usually termed 
a slip and is accompanied by more or less of a 
so-called explosion and a certain amount of 
stock is often thrown from the furnace, while the 
shock may be so severe as to entirely raise the 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 

furnace top. There is much discussion as to 
the true underlying cause of this apparent 
explosion. By some it is thought due to the 
sudden release of the pressure of the trapped 
blast while others believe a true explosion 
occurs. If the latter be the correct assumption 
it may possibly be due to the very finely di- 
vided state of the carbon which, upon access 
to oxygen, may explode at the temperature 
involved in a manner not dissimilar to a so- 
called "dust" explosion. 

The prevention of wedging obviously lies 
primarily in a proper design of the lines of the 
furnace and in carrying such a burden as does 
not require too large a proportion of ore deposit- 
ing excessive carbon. The use of increased 
quantities of limestone with such ores is said 
to mitigate the condition through the solvent 
action of the CO2 gas given off as the ore 
is heated. It has, however, the disadvantage 
of correspondingly increasing the fuel con- 
sumption. 

Chilling — The chilling of the hearth 
naturally results from whatever may cause an 
insufficient supply of heat at that place and 
may result from insufficient fuel supply, leaky 
tuyeres or the falling into the hearth of large 
masses of comparatively cold stock, due to a 
severe slip. 

The remedy depends on the severity of the 
chill. If due to too little fuel, the cooling of the 

142 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

hearth is gradual and may again be brought to 
the proper temperature by the charging of coke 
blanks. If merely local, as for instance, a hard 
tapping hole due to leakage of a tuyere or plate 
near the front of the furnace, the tapping hole 
may be opened with an oxyhydrogen blow 
pipe, oil burner or electric arc. 

If the whole hearth is chilled, as may be 
the case where a mass of stock is precipitated 
into it, every opening may be closed due 
to the displacement of the metal and slag, 
and the only way is to cut out the cinder notch 
and possibly a couple of tuyeres to provide an 
opening for the blast and an escape for the 
products of fusion, gradually working the hearth 
back to its normal condition with the aid of 
the hot blast from the two tuyeres, and with 
others, as fast as they can be brought into 
commission. 



143 




FURNACE REACTIONS 



CHAPTER VI 

GENERAL DISCUSSION 

LTHOUGH the results of the reactions 
/r\\ which occur in the chemistry of the 
blast furnace may be very simply 
expressed and in few equations, yet 
the exact steps involved in arriving at these 
results and the precise order of their precedence 
are matters which experiment and investigation 
of the future will undoubtedly considerably 
develop. The occurrence or non-occurrence 
of certain reactions in given zones is so much 
dependent on the exact temperature of that 
zone, and so interrelated are the many re- 
actions, a number of them occurring simul- 
taneously at various phases of the process, 
that the simple equations by which the results 
are expressed are sometimes misleading as to 
the complexity of the reactions going on within 
the furnace. 

We have to deal only with the three members 
of the charge entering at the top — the ore, 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

flux and fuel, and the air blown in through the 
tuyeres at the bottom. This air may be at the 
temperature of the atmosphere, cold blast, so- 
called, although now seldom used, and on no 
large furnaces; or the hot blast at a temperature 
varying from 800° to 1000° F. or even 1300° or 
1400° F. although the latter is seldom regularly 
maintained in practice in this country. This 
hot air blown through the tuyeres at a pressure 
of from 5 lbs. to 15 lbs. per square inch meets 
the glowing coke before the tuyeres, and the 
oxygen of the air immediately unites with the 
carbon of the coke and forms carbonic acid 
gas, CO2 • This gas, however, is at once changed 
to the monoxide on coming in contact with the 
surrounding particles of incandescent coke, 
i.e., CO2 + C = 2 CO. Whatever water may 
be in the air as vapor is decomposed in contact 
with the incandescent carbon, the oxygen 
uniting with the carbon, leaving free hydrogen. 
This series of reactions, which is nothing more 
or less than that of the gas producer, is very 
simply expressed as follows: 

1st. Carbon burned to carbon dioxide. 

C + 2 O = C0 2 
2d. Reduction of carbon dioxide by hot 

coke. 

C0 2 + C = 2 CO 
3d. Incandescent carbon decomposing 

water and combining with oxygen. 

C + H 2 = CO + H 2 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 



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FROM CAMPBELL 
146 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

The comparatively inert nitrogen of the 
air remains as a whole unchanged and merely 
dilutes the other gases, although this is not 
strictly true, as will be later considered. This 
then, is the composition of the heated volume of 
gases rising to mingle with the descending 
charge of ore, fuel and flux — the composition, 
that is, except as modified by changes in and the 
effect of reactions upon members of the charge 
itself. By volume, just above the tuyeres it is 
about 37% carbon monoxide, CO, with the 
balance nitrogen, save for perhaps 1% hydrogen 
and hydrocarbons. So important is the tem- 
perature in determining the various reactions 
occurring during the descent of the charge that 
these are shown in the accompanying diagram, 
page 146, as indicated by Campbell forwhat may 
be called a standard type of 90' furnace. The 
temperatures and their relative depths are 
indicated, but it should be borne in mind that 
these are by no means absolute, but vary with 
the height of the furnace, its lines, character of 
ores and burden, and the rate at which the 
furnace is driven. Moreover, the temperature 
shown at the tuyeres as 2732° F. in general is 
conceded to be about 3500° F. much nearer the 
theoretical temperature at that point. 

Flux — Considering in detail the changes 
occurring in the various constituents of the 
charge, the flux will be the first considered. 

As noted before, this may be either a 
comparatively pure limestone, CaCOs, or a 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 

magnesian limestone more or less closely 
approaching the composition of a true dolomite. 
As the stone is charged into the furnace, it is 
at first entirely unaffected by the top temper- 
ature, say 500° F. save for the gradual absorp- 
tion of heat. Neither is it affected by any 
chemical action of the gases encountered. As 
it descends, however, acquiring constantly in- 
creasing temperature, it comes to a point where, 
due to this heat, its dissociation begins accord- 
ing to the equation: — CaCOs = CaO + CO2. 

Under normal atmospheric pressure, this 
change begins to occur at about 1050° F. 
although it does not become complete much 
under 1500° F. the temperature of 1050° F. 
corresponding to a depth in the furnace of 
approximately 20'. However, as the gases in 
the furnace have added to the normal atmos- 
pheric pressure, that of the blast at an average 
of possibly 8 to 10 pounds, so the temperature 
must be correspondingly increased, and under 
actual blast furnace conditions, its dissociation 
probably begins at about 1100° F. but is 
uncompleted until practically 1600° F. is 
reached. These temperatures correspond with 
a depth of about 20' and 45' respectively, 
so that from the time the limestone reaches a 
depth of 20', CO2 gas begins to be released, 
the action becoming livelier as the temperature 
rises and is completed at a depth of 45', leaving 
the oxide CaO to continue its descent, steadily 

148 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

absorbing more heat until it reaches the zone 
of fusion well above the tuyeres. Here it 
unites with the silicious portion of the gangue 
and the ash of the coke, and the whole softens 
and melts, dropping as slag or cinder to the 
hearth. 

The carbonic acid gas, CO2, which has been 
liberated during the descent of the stone, has 
mingled and risen with the volume of heated 
gases rushing upward through the shaft of 
the furnace, and has been by no means in- 
active. The action is identical with that 
occurring in the case of CO2 gas formed by the 
combustion of the atmospheric oxygen and the 
carbon of the coke, as the blast enters the 
furnace, i.e., that of the so-called ''carbon 
transfer" or the breaking down of the CO2 
in contact with the incandescent coke into CO. 

C0 2 + C = 2 CO 

This occurs under furnace conditions, at all 
temperatures over approximately 750° F. or 
from 15' to 20' from the top of the furnace, 
while, as we have seen, the zone through which 
the carbon dioxide is given off from the stone, 
has its beginning about 20' from the top and 
extends to a depth of possibly 45' or more. 
Thus, throughout this whole distance, or until 
the gases are cooled below 750° F. the hot 
coke is in this way robbed of just so much of 
its carbon, an abstraction of heat units for 
which no return is made. It is an absolute loss 

149 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 

so far as the economy of operation of the furnace 
is concerned, but passing off through the down- 
comer, its energy is again available in the 
burning of the gases in stoves, in the gas engine 
or under the boilers. 

Fuel — The coke is the least affected of any 
of the members of the charge in its descent. 
Save for the comparatively small amounts of 
carbon abstracted by the CO2 generated by the 
decomposition of the stone, the coke arrives 
almost at the level of the tuyeres in its original 
condition except for the absorption of heat. 
Here it is burned, the carbon reduced to CO 
rising with the ascending column of gas and its 
ash unites with the flux and is incorporated 
in the slag. 

Ore — The reduction of the ore, usually 
an oxide of iron, is effected by both carbonic 
oxide, CO, and by carbon. The exact order 
in which the various reactions resulting in this 
reduction occur, and their thoroughness, de- 
pend both upon the temperature and upon the 
composition of the gases in contact with the 
ore. 

In general, most of the change occurs in 
the upper part of the furnace and begins at 
temperatures considerably lower than those at 
which either coke or limestone are affected. 
With the more easily reducible ores, deoxi- 
dation by CO gas begins between 400° F. and 
500° F. but is much more active at from 800° 

150 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

to 900° F. The reduction due to carbon does 
not begin until a temperature of about 750° F. 
is reached. 

As the ore descends in the furnace and 
reduction becomes more nearly complete, it is 
left in the form of very finely divided metallic 
iron or iron sponge, impregnated with more 
or less carbon deposited during the reduction. 
Upon arriving at the zone of fusion, slightly 
above the tuyeres, this iron sponge becomes 
plastic and finally melts, absorbing a portion 
of the impregnating carbon, and drops through 
the accumulated slag to the hearth. 

The reactions which occur in the process, 
as briefly outlined, are simple ones, but the 
exact order of their occurrence and the degree 
to which each is completed at any given stage, 
are by no means easy to determine. 

The following equations represent the action 
of carbonic oxide on the oxides of iron en- 
countered : 

(a) 3 Fe 2 3 + CO = 2 Fe 3 4 + C0 2 

(b) Fe 3 4 + CO = 3 FeO + C0 2 

(c) FeO + CO = Fe + C0 2 

The results of the above reactions may be 
expressed as follows: 

Fe 2 3 + 3 CO = Fe 2 + 3 C0 2 
Unfortunately, reduction is actually com- 
pleted by no means as simply as this, because 
by a change of temperature the product of 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

equations (b) and (c), i.e., FeO and Fe, may in 
turn be oxidized by the carbon dioxide liberated 
in their formation. Such reoxidation may be 
expressed by the following equations : 

(d) 2 FeO + C0 2 = Fe 2 3 + CO 

(e) 2 Fe + 3 C0 2 = Fe 2 3 + 3 CO 

The reactions of C0 2 upon the metallic 
sponge and the lower oxides begin, according 
to Campbell, at 570° F. although more active 
at higher temperatures and varying with the 
relative amounts of C0 2 and CO in the gases 
present. Since CO2 is a necessary product in 
the equation by which the iron ore is reduced, 
it is evident that the reduction can never be 
wholly completed by the action of CO alone, 
as the CO2 evolved will, at high temperatures, 
reoxidize to some extent the metallic iron. 
The excess of CO, however, whose presence is 
due to the carbon transfer allows this reduction 
to be much more nearly complete than would 
otherwise be possible. 

For the completion of this reduction, we must 
look to the reducing effect of carbon which is 
deposited throughout the mass of the ore as it 
is partially reduced and descends in the furnace. 
There is much discussion in accounting for the 
precise equation involved in its deposition and 
the manner of its occurrence. There is still 
much to be learned. It is claimed by some that 
it is due to the power of the metallic iron or 

152 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

iron sponge and the lower oxides to split up 
the CO gas in accordance with the equation: 

2 CO - C0 2 + C 

In this, the iron does not itself form part of 
the reaction, but acts as a calalytic agent, as 
does the well known platinum sponge in a 
number of familiar instances in the laboratory. 

Others have claimed that deposition can 
occur only by the oxidation of metallic iron 
according to the following equations: 
Fe + CO = FeO + C 

2 Fe + CO2 = 2 FeO + C 

However, deposition begins at about 429° 
F. and at that temperature metallic iron has 
not yet been reduced from the ore except by a 
reaction which itself produces carbon dioxide. 
Neither does CO2 react upon metallic iron 
until a temperature of over 500° F. Although 
either of the above equations involving oxidation 
by carbon monoxide or dioxide may account for 
most of the deposition occurring at high temper- 
atures, the only reaction which can occur at 
the temperature at which deposited carbon is 
first actually found is: 

2 Fe 2 3 +.8 CO = 7 COa + 4 Fe +"C 

Whatever the reactions involved, its 
deposition becomes more active as the temper- 
ature is raised, but ceases at about 1000° F. 
and it is probably this carbon which removes 
the last traces of oxygen, completing the 

153 



Harbison- Walker Refractories Co., Pittsburgh, Pa. 

work of the CO. The reactions between the 
oxides and carbon are expressed as follows: 

Fe 2 3 +3C = 2Fe + 3CO 

Fe 3 4 + 4 C = 3 Fe + 4 CO 

FeO + C - Fe + CO 

The matter of the deposition of carbon is a 
most important one, both on account of the 
reducing effect of the carbon itself and the effect 
its deposition has in disintegrating the ores. 
Its reducing powder is evident at all temper- 
atures above about 720° F. The quantity 
evolved in the reduction of various ores is 
apparently much dependent upon the mineralog- 
ical classification of the ores, Laudig finding the 
following maximum and minimum: 

Maximum Minimum 

Mesabi Ores 36.40 10.20 

Brown Hematites. . 24.92 .98 

Magnetites Practically nil. 

The above figures are the weights of carbon 
deposited in per cent, weight of the ore, and 
indicate that the mass of the ore is thus some- 
times increased two or three times the original 
volume. There is no question but that the 
porosity of the ore has an important bearing 
on its ease of reduction, possibly due to the fact 
that the carbon may thus be more easily 
deposited throughout its mass and effect its 
work of reduction. It may also partially 
explain the fact of the greater difficulty usually 
encountered in the reduction of the Magnetites. 

154 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

The value of the more easily reducible ores, 
such as those of the Mesabi range, is seen from 
the fact that the greater part of this reduction 
and the consequent liberation of CO2 gas takes 
place in the upper zone of the furnace and at a 
temperature at which the gas does not react 
upon the coke, CO2 passing out of the furnace 
without being reduced to CO, with the conse- 
quent expenditure of heat and higher fuel 
consumption due to it. Conversely, the higher 
fuel consumption with Magnetite ores, is also 
undoubtedly explained by the higher temper- 
ature and consequent greater depth at which 
its reduction occurs. 

The carbon deposit is subject to the solvent 
action of CO2 at temperatures of about 760° F. 
and above, so that a very considerable portion 
of it may be thus dissolved during its journey 
through the furnace although the deposition 
itself ceases, as has been mentioned, at about 
1000° F. Were it not for this fact, there would 
undoubtedly occur great trouble in scaffolding 
and clogging of the descending mass, due to its 
great increase in volume; such trouble is in 
fact by no means uncommon with the very fine 
and easily reducible ores. 

As a summary of the changes occurring in 
the blast furnace, the graphic representation 
shown on page 146 may again be referred to. 

155 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 




40V REDUdTiON BY 
' OXIDATJION of C. 




3550° > 



DEGREES FAHRENHEIT 



Temperature Gradient of Blast Furnace. 



FROM FORSYTHE 



156 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

This figure shows not only the general order of 
occurrence but the degree to which each re- 
action is completed under the usual conditions 
existing at any given level in the furnace. 

There are differences of opinion, however, 
among a number of authorities as to some of the 
points as indicated on this diagram particularly 
as regards the progress of reduction of the ore. 
In accordance with BeTs experiments it ap- 
parently often occurs, as a whole, at higher 
levels than as shown in this diagram. Lime- 
stone, too, was by no means always entirely 
decomposed at 32' from the top, but at times 
persisted well below the upper bosh line. 

Deposited carbon is usually assumed to be 
mere nearly absorbed by CO2 than as indicated 
and the temperature at the tuyeres or just 
above is, in a majority of cases, considerably 
higher than here shown. 

As showing the temperatures usually con- 
sidered more representative of average modern 
practice, the accompanying diagram showing 
the temperature gradient, as given in Forsythe's 
work, will be of interest. 

Cyanides — Although the greater portion 
of the nitrogen of the air entering the furnace 
as blast may be considered as inert, yet a certain 
part unites with the incandescent carbon of the 
coke, forming cyanogen, Cn, which in turn 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

combines with whatever sodium and potassium 
may be present, forming cyanides. Owing to 
the affinity of the cyanides for oxygen with the 
formation of cyanates, their action, whatever 
it may be quantitatively, is actively reducing 
in its nature. The cyanates are volatile and 
join the rising volume of gases until decom- 
posed by carbon dioxide, leaving the carbonate 
as deposited in the upper portions of the furnace. 
This carbonate may be carried down by the 
descending charge and again combine with 
cyanogen near the tuyeres. There is thus an 
ever increasing quantity of cyanides present 
and to them is attributed by some the improve- 
ment in the running during the period following 
the blowing in of the furnace. 

Carbon Ratio — This term is used to ex- 
press the ratio of the CO in the escaping gases 

CO 

to the CO2. The ratio has a direct rela- 

C0 2 

tion to fuel consumption inasmuch as the greater 

the proportion of C0 2 the greater the heat 

developed in the furnace, and the less heat 

units escape as CO. It means, however, that the 

greater the dilution of CO, the reducing gas, 

the less the reducing power in the gases. The 

ratio is often brought below^ 1.5, however, with 

good results from the standpoint of reduction. 

The following table from Forsythe gives 

representative analyses of these gases and is of 

158 



Harbison-Walker Refractories Co., Pittsburgh, Pa. 

interest as showing their variation at the several 

levels: 

Per cent, by Volume 

Depth CO. C0 2 . 
Feet 

Top 29.5 11.0 

4 29.5 10.5 

8 27.0 8.0 

10 32.0 7.0 

12 33.0 7.0 

14 31.0 6.5 

163^ 34.1 2.2 

20 35.1 0.7 

39 35.0 1.1 

52 35.2 1.5 

65 35.9 0.5 

70y 2 36.6 0.0 

Tuyeres 37.7 0.8 

Dry-Air Blast — In considering this phase 
of modern blast furnace practice, it should be 
realized that it is in no sense a mere theoretical 
refinement, but aims to regulate the one big 
variable in the operation of the blast furnace. 
All the other materials, the ore, stone and coke 
vary at the most but a few per cent, in their 
composition from time to time, while the 
moisture in the air may vary more than 100% 
from day to day, and of this air the production 
of a ton of iron requires almost double the 
weight of the other raw materials. 

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Harbison- Walker Refractories Co., Pittsburgh, Pa. 

As Gayley points out, 1 grain of moisture 
per cubic foot of air means practically a 
gallon of water per hour for each thousand 
cubic feet of air per minute, blown into the 
furnace. In other words, for a furnace blowing 
35,000 feet of air per minute, not a large 
furnace, there would be blown in 35 gallons of 
water per hour for each grain of water per 
cubic foot in the atmosphere. 

The amount of this vapor in the atmosphere 
varies with the temperature and humidity, the 
average the year through for Pennsylvania, 
for instance, being about 55° F. and a humidity 
of 70%. At 55° F. the atmosphere, if saturated, 
would have 4.92 grains of moisture per cubic 
foot; at 70% humidity, 3.44 grains per cubic 
foot. 

In the so-called dry blast a large portion of 
the moisture in the atmosphere is removed by 
refrigeration previous to the introduction of the 
air into the stoves. Any moisture on entering 
the furnace at the temperature encountered at 
the tuyeres is immediately dissociated by the 
intense heat into the component gases: — 
H 2 = 2 H + O. In doing this, it absorbs 
the same amount of heat as is generated in 
burning hydrogen to make an equivalent 
quantity of water. In other words, in accord- 
ance with the atomic weights of the elements, 
if 18 parts of water by weight are dissociated, 
they will make 2 parts by weight of hydrogen 

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Harbison-Walker Refractories Co., Pittsburgh, Pa. 

and 16 parts by weight of oxygen, absorbing 
the same heat as generated by burning 2 parts 
by weight of hydrogen. Two pounds of 
hydrogen on burning to the condition of steam, 
give off 103,500 B.T.U., or this is the heat 
absorbed by the dissociation of 18 parts of 
steam, or for each pound, 5,750 B.T.U. 

However, on the credit side should be placed 

the heat gained by the burning of the oxygen 

evolved to CO, C + O = CO. This heat 

equivalent equals, 

12 

— X 4450 B.T.U. = 2965 B.T.U's per lb. 

[steam. 

5750 — 2965 = 2785 B.T.U. 

This is the net loss by absorption per pound of 

vapor in the blast. 

The amount of air necessary to burn the 
fuel for smelting 100 pounds of pig varies 
w^ith the temperature of the blast, but a fair 
average may be taken at 5300 cubic feet. 
With the amount of moisture contained under 
average conditions, as previously assumed for 
Pennsylvania (3.44 grains) the total moisture 
will then be: 

5300 X 3.44 

7000 (grains per lb.) 

2780 B.T.U X 2.6 = 7235 B.T.U. 

The above figure represents the heat lost 
per hundred pounds of iron smelted, due to the 
moisture in the atmosphere or, expressed in 

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Harbison-Walker Refractories Co., Pittsburgh, Pa. 

coke consumption, somewhat over 50 pounds 
of coke per ton of pig made. 

The Gayley process, as installed at saveral 
plants, has removed by cooling to 25° or 30° 
F. approximately 65 to 70 pounds of water 
per ton of pig smelted during some of the 
more humid months of the year, a theoretical 
saving in the consumption of coke of some 55 
pounds per ton of iron, but the actual saving 
has proven far greater. 

A brief summary of the results as covered 
in Gayley's paper on the Application of Dry- 
Air Blast to the Manufacture of Pig Iron, shows 
the following: 

Natural blast, Aug. Dry blast, Aug. 25- 
1-11, inclusive. Sept. 9, inclusive. 

Average moisture 5.66 grs. psrcu. ft. 1.75 grs. per cu. ft. 

Average daily out- 
put 358 tons 447 tons 

Average fuel con- 
sumption 2,147 pounds 1,726 pounds 

Cubic feet air 40,000 per min. 34,000 per min. 

Temperature of blast 720 degrees F. 870 degrees F. 

CO in gases 22.3 per cent. 19.9 per cent. 

C0 2 in gases 13.0 per cent. 16.0 per cent. 

Temperature of gases 538 degrees F. 376 degrees F. 

Flue dust 5.0 per cent. 1.0 per cent. 

From this it will be seen that the actual 
saving far exceeds any that can theoretically 
be accounted for either by the mere elimination 
of moisture or rise in temperature of the blast. 

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Harbison-Walker Refractories Co., Pittsburgh, Pa. 

There has been much discussion regarding it, 
but probably the greatest saving is in reality 
attributable to the securing of uniformly 
favorable operating conditions. Regularity is a 
prime essential for economical running and 
with these conditions uniformly good there is 
no need for the excess fuel necessary to provide 
for contingencies. 

It would not, however, be the part of wisdom 
to assume that such enormous saving could be 
made at all plants and under all conditions, 
but it is probably safe to say that the average 
plant can decrease its coke consumption at 
least 12% and increase the production 10%, 
while in very many cases it is perfectly feasible 
to raise these percentages to 14% and 12% 
respectively. This, of course, refers to what 
may be relied upon the year through and not 
merely for short periods under the stress of 
record breaking output. 



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The Caxton Company 
Cleveland 



